N-methyl-D-aspartate receptor modulators and methods of making and using same

ABSTRACT

Disclosed are compounds having enhanced potency in the modulation of NMDA receptor activity. Such compounds are contemplated for use in the treatment of diseases and disorders, such as learning, cognitive activities, and analgesia, particularly in alleviating and/or reducing neuropathic pain. Orally available formulations and other pharmaceutically acceptable delivery forms of the compounds, including intravenous formulations, are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. § 371PCT patent application PCT/US2015/042070, filed on Jul. 24, 2015, whichclaims priority to and the benefit of U.S. Patent Application No.62/129,388, filed Mar. 6, 2015, and U.S. Patent Application No.62/028,512, filed Jul. 24, 2014, the disclosures of which are herebyincorporated herein by reference in their entireties.

BACKGROUND

An N-methyl-d-aspartate (NMDA) receptor is a postsynaptic, ionotropicreceptor that is responsive to, inter alia, the excitatory amino acidsglutamate and glycine and the synthetic compound NMDA. The NMDA receptorcontrols the flow of both divalent and monovalent ions into thepostsynaptic neural cell through a receptor associated channel (Fosteret al., Nature 1987, 329:395-396; Mayer et al., Trends in Pharmacol.Sci. 1990, 11:254-260). The NMDA receptor has been implicated duringdevelopment in specifying neuronal architecture and synapticconnectivity, and may be involved in experience-dependent synapticmodifications. In addition, NMDA receptors are also thought to beinvolved in long term potentiation and central nervous system disorders.

The NMDA receptor plays a major role in the synaptic plasticity thatunderlies many higher cognitive functions, such as memory acquisition,retention and learning, as well as in certain cognitive pathways and inthe perception of pain (Collingridge et al., The NMDA Receptor, OxfordUniversity Press, 1994). In addition, certain properties of NMDAreceptors suggest that they may be involved in theinformation-processing in the brain that underlies consciousness itself.

The NMDA receptor has drawn particular interest since it appears to beinvolved in a broad spectrum of CNS disorders. For instance, duringbrain ischemia caused by stroke or traumatic injury, excessive amountsof the excitatory amino acid glutamate are released from damaged oroxygen deprived neurons. This excess glutamate binds to the NMDAreceptors which opens their ligand-gated ion channels; in turn thecalcium influx produces a high level of intracellular calcium whichactivates a biochemical cascade resulting in protein degradation andcell death. This phenomenon, known as excitotoxicity, is also thought tobe responsible for the neurological damage associated with otherdisorders ranging from hypoglycemia and cardiac arrest to epilepsy. Inaddition, there are preliminary reports indicating similar involvementin the chronic neurodegeneration of Huntington's, Parkinson's, andAlzheimer's diseases. Activation of the NMDA receptor has been shown tobe responsible for post-stroke convulsions, and, in certain models ofepilepsy, activation of the NMDA receptor has been shown to be necessaryfor the generation of seizures. Neuropsychiatric involvement of the NMDAreceptor has also been recognized since blockage of the NMDA receptorCa⁺⁺ channel by the animal anesthetic PCP (phencyclidine) produces apsychotic state in humans similar to schizophrenia (reviewed in Johnson,K. and Jones, S., 1990). Further, NMDA receptors have also beenimplicated in certain types of spatial learning.

The NMDA receptor is believed to consist of several protein chainsembedded in the postsynaptic membrane. The first two types of subunitsdiscovered so far form a large extracellular region, which probablycontains most of the allosteric binding sites, several transmembraneregions looped and folded so as to form a pore or channel, which ispermeable to Ca⁺⁺, and a carboxyl terminal region. The opening andclosing of the channel is regulated by the binding of various ligands todomains (allosteric sites) of the protein residing on the extracellularsurface. The binding of the ligands is thought to affect aconformational change in the overall structure of the protein which isultimately reflected in the channel opening, partially opening,partially closing, or closing.

NMDA receptor compounds may exert dual (agonist/antagonist) effect onthe NMDA receptor through the allosteric sites. These compounds aretypically termed “partial agonists”. In the presence of the principalsite ligand, a partial agonist will displace some of the ligand and thusdecrease Ca⁺⁺ flow through the receptor. In the absence of or loweredlevel of the principal site ligand, the partial agonist acts to increaseCa⁺⁺ flow through the receptor channel.

A need continues to exist in the art for novel and more specific/potentcompounds that are capable of binding the glycine binding site of NMDAreceptors, and provide pharmaceutical benefits. In addition, a needcontinues to exist in the medical arts for an orally deliverable formsof such compounds.

SUMMARY

Provided herein, at least in part, are compounds that are NMDAmodulators, for example, partial agonists of NMDA. For example,disclosed herein are compounds having formula (I):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof,

wherein:

R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R⁵⁵, R⁷⁸, and R^(y) are asdefined below.

In another aspect, a compound of formula (I) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., one orboth of the proline moieties is/are replaced with a beta-amino acid(s);e.g., the C-terminal and/or the N-terminal is/are replaced with abeta-amino acid(s), and one or both of the proline moieties is/arereplaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (I-A), in which formula (I) is modified suchthat the left-most proline moiety is replaced with:

in which R⁷, R⁸, and R⁷⁸ are as defined below. As another example, suchcompounds can have formula (I-B), in which formula (I) is modified suchthat the right-most proline moiety is replaced with:

in which R⁵, R⁶, and R⁵⁵ are as defined below. In still anotherembodiment, compounds are provided, in which any one or more ofcompounds of formula (I), (I-A), and (I-B) are modified such that theleft-most (N-terminal) amino acid is replaced with hydrogen, therebyproviding a tripeptide wherein the ring nitrogen of left-most prolinemoiety is bonded to hydrogen.

In another aspect, a compound is provided having formula (II):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof, wherein:

R¹, R², R³, R⁴, R⁹, R¹⁰, R¹⁵, R¹⁶, R¹⁷, R¹⁸, R^(x), and R^(y) are asdefined below.

In another aspect, a compound of formula (II) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., theproline and/or phenyl alanine moieties is/are replaced with a beta-aminoacid(s); e.g., the C-terminal and/or the N-terminal is/are replaced witha beta-amino acid(s), and the proline and/or phenyl alanine moietiesis/are replaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (II-A), in which formula (II) is modifiedsuch that the proline moiety is replaced with:

in which R¹⁷ and R¹⁸ are as defined below. In still another embodiment,compounds are provided, in which any one or more of compounds of formula(II) and (II-A) are modified such that the left-most (N-terminal) aminoacid is replaced with hydrogen, thereby providing a tripeptide whereinthe ring nitrogen of proline moiety is bonded to hydrogen.

In yet another aspect, a compound is provided having formula (III):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof,

wherein:

R, R′, R⁹, R¹⁰, R²¹, R²², R²³, R^(a), R^(b), R^(c), R^(d), R^(e), R^(f),R^(g), R^(h) and R^(i) are as defined below.

In another aspect, a compound of formula (III) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., theproline and/or trytophan moieties is/are replaced with a beta-aminoacid(s); e.g., the C-terminal and/or the N-terminal is/are replaced witha beta-amino acid(s), and the proline and/or tryptophan moieties is/arereplaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (III-A), in which formula (III) is modifiedsuch that the proline moiety is replaced with:

in which R²¹, R²², and R²³ are as defined below. In still anotherembodiment, compounds are provided, in which any one or more ofcompounds of formula (III) and (III-A) are modified such that theleft-most (N-terminal) amino acid is replaced with hydrogen, therebyproviding a tripeptide wherein the ring nitrogen of proline moiety isbonded to hydrogen.

In yet another aspect, a compound is provided having formula (IV):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof,

wherein:

R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁵⁵, R⁷⁸, and R^(y) are as defined below.

In another aspect, a compound of formula (IV) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., one orboth of the proline moieties is/are replaced with a beta-amino acid(s);e.g., the C-terminal and/or the N-terminal is/are replaced with abeta-amino acid(s), and one or both of the proline moieties is/arereplaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (IV-A), in which formula (IV) is modifiedsuch that the left-most proline moiety is replaced with:

in which R⁷, R⁸, and R⁷⁸ are as defined below. As another example, suchcompounds can have formula (IV-B), in which formula (IV) is modifiedsuch that the right-most proline moiety is replaced with:

in which R⁵, R⁶, and R⁵⁵ are as defined below. In still anotherembodiment, compounds are provided, in which any one or more ofcompounds of formula (IV), (IV-A), and (IV-B) are modified such that theleft-most (N-terminal) amino acid is replaced with hydrogen, therebyproviding a tripeptide wherein the ring nitrogen of left-most prolinemoiety is bonded to hydrogen.

In a further aspect, a compound is provided having formula (V):T¹-P¹-P²-T²  (V)and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof, wherein T¹, P¹, P², and T² are as defined below.

Also provided herein are compounds that are useful, e.g., as syntheticintermediates, e.g.,

In some embodiments, protecting groups other than Cbz can be employedfor compounds of formula (V) e.g., 9-fluorenylmethyloxycarbonyl (Fmoc),tert-butoxycarbonyl (Boc), p-methoxybenzyloxycarbonyl, acetyl,trifluoroacetyl, benzoyl, phthalimido, benzyl (Bn), p-methoxybenzyl,p-methoxyphenyl, 3,4-dimethoxybenzyl, triphenylmethyl, benzylidene, andp-toluenesulfonyl (Ts). In some embodiments, the hydroxyl group of thecompounds shown above can also be protected, e.g., with an alkyl orsilyl group (thereby forming the corresponding alkyl or silyl ether) oracyl (e.g., CH₃C(O)—, thereby forming an ester).

In certain embodiments, protecting groups employed in the compounds offormula (V) can have the following formula: —C(O)OR_(PG1), whereinR_(PG1) is selected from the group consisting of: C₁-C₆ alkyl; C₁-C₆haloalkyl; C₂-C₆ alkenyl; C₂-C₆ alkynyl; C₃-C₁₀ cycloalkyl, wherein theC₃-C₁₀ cycloalkyl is optionally substituted with from 1-3 independentlyselected C₁-C₃ alkyl; —CH₂—C₃-C₁₀ cycloalkyl wherein the C₃-C₁₀cycloalkyl is optionally substituted with from 1-3 independentlyselected C₁-C₃ alkyl; —CH₂-phenyl, wherein the phenyl is optionallysubstituted with from 1-2 substituents independently selected from C₁-C₃alkyl, C₁-C₃ haloalkyl, C₁-C₃ alkoxy, C₁-C₃ haloalkoxy, nitro, halo,SO₂Me, cyano, and —OC(O)CH₃; and —CH₂-pyridyl.

In other embodiments, protecting groups employed in the compounds offormula (V) can have the following formula: —C(O)R_(PG2), wherein R₃₂ isselected from the group consisting of: H; C₁-C₆ alkyl; C₁-C₆ haloalkyl;phenyl, wherein the phenyl is optionally substituted with from 1-2substituents independently selected from C₁-C₃ alkyl; C₁-C₃ haloalkyl;C₁-C₃ alkoxy; C₁-C₃ haloalkoxy; nitro; halo; SO₂Me, cyano; and—OC(O)CH₃; and pyridyl.

Also provided herein are pharmaceutically acceptable compositionscomprising a disclosed compound, and a pharmaceutically acceptableexcipient. For example, such compositions may be suitable for oraladministration to a patient. In other embodiments, such compositions maybe suitable for injection. Compounds can also include any compounddisclosed in the schemes, tables, and figures provided herein.

In another aspect, a method of treating autism, in a patient in needthereof, is provided comprising administering to the patient apharmaceutically effective amount of a contemplated compound.

In yet another aspect, a method of treating a condition selected fromthe group consisting of epilepsy, AIDS dementia, multiple systematrophy, progressive supra-nuclear palsy, Friedrich's ataxia, Down'ssyndrome, fragile X syndrome, tuberous sclerosis,olivio-ponto-cerebellar atrophy, cerebral palsy, drug-induced opticneuritis, peripheral neuropathy, myelopathy, ischemic retinopathy,diabetic retinopathy, glaucoma, cardiac arrest, behavior disorders, andimpulse control disorders, in a patient in need thereof, is providedcomprising administering to the patient a pharmaceutically effectiveamount of a contemplated compound.

In still another aspect, a method of treating a condition selected fromthe group consisting of attention deficit disorder, ADHD, schizophrenia,depression, anxiety, amelioration of opiate, nicotine, and/or ethanoladdiction, traumatic brain injury, spinal cord injury, post-traumaticstress syndrome, and Huntington's chorea, in a patient in need thereof,is provided comprising administering to the patient a pharmaceuticallyeffective amount of a contemplated compound.

In yet another aspect, a method of treating Alzheimer's disease, ormemory loss that accompanies early stage Alzheimer's disease in apatient in need thereof, is provided comprising administering to thepatient a pharmaceutically effective amount of a contemplated compound.

In still another aspect, a method of treating Huntington's disease, in apatient in need thereof, is provided comprising administering to thepatient a pharmaceutically effective amount of a contemplated compound.

In some embodiments, a contemplated compound may be administered to apatient in need thereof intravenously, intraperitoneally, intranasally,orally, intramuscularly, or subcutaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the chemical structure of an exemplary formula (III)compound.

FIG. 2 is a series of matrices showing the chemical structures of 1exemplary formula (III) compounds that contain unnatural amino acidprecursors; the non-natural proline portion is shown in the tophorizontal row of each matrix, and the non-natural proline portion isshown in the top horizontal row of each matrix.

FIG. 3 shows the chemical structures of exemplary non-natural left-handfragments that can be used to prepare the compounds described herein.

FIG. 4 shows the chemical structure of an exemplary formula (III)compound.

FIG. 5 shows the results of glycine dose response in the presence of 50μM glutamate.

FIG. 6 shows a transformation of the glycine dose response to determinethe absolute background.

FIG. 7 shows a compound dose response performed using the [³H]MK-801assay described herein.

DETAILED DESCRIPTION

This disclosure is generally directed to compounds that are capable ofmodulating NMDA, e.g., NMDA antagonists or partial agonists, andcompositions and/or methods of using the disclosed compounds.

Definitions

In some embodiments, the compounds, as described herein, may besubstituted with any number of substituents or functional moieties. Ingeneral, the term “substituted” whether preceded by the term“optionally” or not, and substituents contained in formulas, refer tothe replacement of hydrogen radicals in a given structure with theradical of a specified substituent.

In some instances, when more than one position in any given structuremay be substituted with more than one substituent selected from aspecified group, the substituent may be either the same or different atevery position.

As used herein, the term “substituted” is contemplated to include allpermissible substituents of organic compounds. In a broad aspect, thepermissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, aromatic and non-aromaticsubstituents of organic compounds. In some embodiments, heteroatoms suchas nitrogen may have hydrogen substituents and/or any permissiblesubstituents of organic compounds described herein which satisfy thevalencies of the heteroatoms. Non-limiting examples of substituentsinclude acyl; aliphatic; heteroaliphatic; aryl (e.g., phenyl);heteroaryl; arylalkyl; heteroarylalkyl; alkoxy; cycloalkoxy;heterocyclylalkoxy; heterocyclyloxy; heterocyclyloxyalkyl; alkenyloxy;alkynyloxy; aryloxy; heteroalkoxy; heteroaryloxy; alkylthio; arylthio;heteroarylthio; oxo; —F; —Cl; —Br; —I; —OH; —NO₂; —N₃; —CN; —SCN;—SR^(x); —CF₃; —CH₂CF₃; —CHCl₂; —CH₂OH; —CH₂CH₂OH; —CH₂NH₂; —CH₂SO₂CH₃;—OR^(x), —C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂;—OC(O)R^(x); —OCO₂R^(x); —OC(O)N(R^(x))₂; —N(R^(x))₂; —SOR^(x);—S(O)₂R^(x); —NR^(x)C(O)R^(x); —NR^(x)C(O)N(R^(x))₂; —NR^(x)C(O)OR^(x);—NR^(x)C(NR^(x))N(R^(x))₂; and —C(R^(x))₃; wherein each occurrence ofR^(x) independently includes, but is not limited to, hydrogen, halogen,acyl, aliphatic, heteroaliphatic, aryl, heteroaryl, arylalkyl, orheteroarylalkyl, wherein any of the aliphatic, heteroaliphatic,arylalkyl, or heteroarylalkyl substituents described above and hereinmay be substituted or unsubstituted, branched or unbranched, cyclic oracyclic, and wherein any of the aryl or heteroaryl substituentsdescribed above and herein may be substituted or unsubstituted.Furthermore, the compounds described herein are not intended to belimited in any manner by the permissible substituents of organiccompounds. In some embodiments, combinations of substituents andvariables described herein may be preferably those that result in theformation of stable compounds. The term “stable,” as used herein, refersto compounds which possess stability sufficient to allow manufacture andwhich maintain the integrity of the compound for a sufficient period oftime to be detected and preferably for a sufficient period of time to beuseful for the purposes detailed herein.

The term “aliphatic,” as used herein, includes both saturated andunsaturated, straight chain (i.e., unbranched), branched, acyclic,cyclic, or polycyclic aliphatic hydrocarbons, which are optionallysubstituted with one or more functional groups. As will be appreciatedby one of ordinary skill in the art, “aliphatic” is intended herein toinclude, but is not limited to, alkyl, alkenyl, alkynyl, cycloalkyl,cycloalkenyl, and cycloalkynyl moieties.

The terms “aryl” and “heteroaryl,” as used herein, refer to mono- orpolycyclic unsaturated moieties having preferably 3-14 carbon atoms,each of which may be substituted or unsubstituted. In certainembodiments, “aryl” refers to a mono- or bicyclic carbocyclic ringsystem having one or two aromatic rings including, but not limited to,phenyl, naphthyl, tetrahydronaphthyl, indanyl, indenyl, and the like. Incertain embodiments, “heteroaryl” refers to a mono- or bicyclicheterocyclic ring system having one or two aromatic rings in which one,two, or three ring atoms are heteroatoms independently selected from thegroup consisting of S, O, and N and the remaining ring atoms are carbon.Non-limiting examples of heteroaryl groups include pyridyl, pyrazinyl,pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl, thiazolyl, oxazolyl,isooxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl, furanyl, quinolinyl,isoquinolinyl, and the like.

The term “alkenyl” as used herein refers to an unsaturated straight orbranched hydrocarbon having at least one carbon-carbon double bond, suchas a straight or branched group of 2-12, 2-10, or 2-6 carbon atoms,referred to herein as C₂-C₁₂alkenyl, C₂-C₁₀alkenyl, and C₂-C₆alkenyl,respectively. Exemplary alkenyl groups include, but are not limited to,vinyl, allyl, butenyl, pentenyl, hexenyl, butadienyl, pentadienyl,hexadienyl, 2-ethylhexenyl, 2-propyl-2-butenyl,4-(2-methyl-3-butene)-pentenyl, etc.

The term “alkoxy” as used herein refers to an alkyl group attached to anoxygen (—O-alkyl). Exemplary alkoxy groups include, but are not limitedto, groups with an alkyl group of 1-12, 1-8, or 1-6 carbon atoms,referred to herein as C₁-C₁₂alkoxy, C₁-C₈alkoxy, and C₁-C₆alkoxy,respectively. Exemplary alkoxy groups include, but are not limited tomethoxy, ethoxy, etc. Similarly, exemplary “alkenoxy” groups include,but are not limited to vinyloxy, allyloxy, butenoxy, etc. The term“cycloalkoxy” as used herein refers to an cycloalkyl group attached toan oxygen (—O-cycloalkyl).

The term “alkoxycarbonyl” as used herein refers to a straight orbranched alkyl group attached to oxygen, attached to a carbonyl group(alkyl-O—C(O)—). Exemplary alkoxycarbonyl groups include, but are notlimited to, alkoxycarbonyl groups of 1-6 carbon atoms, referred toherein as C₁₋₆alkoxycarbonyl. Exemplary alkoxycarbonyl groups include,but are not limited to, methoxycarbonyl, ethoxycarbonyl,t-butoxycarbonyl, etc.

The term “alkynyloxy” used herein refers to a straight or branchedalkynyl group attached to an oxygen (alkynyl-O)). Exemplary alkynyloxygroups include, but are not limited to, propynyloxy.

The term “alkyl” as used herein refers to a saturated straight orbranched hydrocarbon, for example, such as a straight or branched groupof 1-6, 1-4, or 1-3 carbon atom, referred to herein as C₁-C₆alkyl,C₁-C₄alkyl, and C₁-C₃alkyl, respectively. Exemplary alkyl groupsinclude, but are not limited to, methyl, ethyl, propyl, isopropyl,2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl,3-methyl-1-butyl, 2-methyl-3-butyl, 2,2-dimethyl-1-propyl,2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl,2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl,2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, butyl,isobutyl, t-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl,etc.

The term “alkylcarbonyl” as used herein refers to a straight or branchedalkyl group attached to a carbonyl group (alkyl-C(O)—). Exemplaryalkylcarbonyl groups include, but are not limited to, alkylcarbonylgroups of 1-6 atoms, referred to herein as C₁-C₆alkylcarbonyl groups.Exemplary alkylcarbonyl groups include, but are not limited to, acetyl,propanoyl, isopropanoyl, butanoyl, etc.

The term “alkynyl” as used herein refers to an unsaturated straight orbranched hydrocarbon having at least one carbon-carbon triple bond, suchas a straight or branched group of 2-6, or 3-6 carbon atoms, referred toherein as C₂₋₆alkynyl, and C₃₋₆alkynyl, respectively. Exemplary alkynylgroups include, but are not limited to, ethynyl, propynyl, butynyl,pentynyl, hexynyl, methylpropynyl, etc.

Alkyl, alkenyl and alkynyl groups can optionally be substituted, if notindicated otherwise, with one or more groups selected from alkoxy,alkyl, cycloalkyl, amino, halogen, and —C(O)alkyl. In certainembodiments, the alkyl, alkenyl, and alkynyl groups are not substituted,i.e., they are unsubstituted.

The term “amide” or “amido” as used herein refers to a radical of theform —R^(a)C(O)N(R^(b))—, —R^(a)C(O)N(R^(b))R^(e)—, or —C(O)NR^(b)R^(e),wherein R^(a), R^(b), and R^(e) are each independently selected fromalkoxy, alkyl, alkenyl, alkynyl, amide, amino, aryl, arylalkyl,carbamate, cycloalkyl, ester, ether, formyl, halogen, haloalkyl,heteroaryl, heterocyclyl, hydrogen, hydroxyl, ketone, and nitro. Theamide can be attached to another group through the carbon, the nitrogen,R^(b), R^(c), or R^(a). The amide also may be cyclic, for example R^(b)and R^(c), R^(a) and R^(b), or R^(a) and R^(e) may be joined to form a3- to 12-membered ring, such as a 3- to 10-membered ring or a 5- to6-membered ring. The term “carboxamido” refers to the structure—C(O)NR^(b)R^(e).

The term “amine” or “amino” as used herein refers to a radical of theform —NR^(d)R^(e), where R^(d) and R^(e) are independently selected fromhydrogen, alkyl, alkenyl, alkynyl, aryl, arylalkyl, cycloalkyl,haloalkyl, heteroaryl, and heterocyclyl. The amino also may be cyclic,for example, R^(d) and R^(e) are joined together with the N to form a 3-to 12-membered ring, e.g., morpholino or piperidinyl. The term aminoalso includes the corresponding quaternary ammonium salt of any aminogroup, e.g., —[N(R^(d))(R^(e))(R^(f))]+. Exemplary amino groups includeaminoalkyl groups, wherein at least one of R^(d), R^(e), or R^(f) is analkyl group. In certain embodiment, R^(d) and R^(e) are hydrogen oralkyl.

The term “cycloalkyl” as used herein refers to a monocyclic saturated orpartially unsaturated hydrocarbon group of for example 3-6, or 4-6carbons, referred to herein, e.g., as C₃₋₆cycloalkyl or C₄₋₆cycloalkyland derived from a cycloalkane. Exemplary cycloalkyl groups include, butare not limited to, cyclohexyl, cyclohexenyl, cyclopentyl, cyclobutylor, cyclopropyl.

The terms “halo” or “halogen” or “Hal” as used herein refer to F, Cl,Br, or I. The term “haloalkyl” as used herein refers to an alkyl groupsubstituted with one or more halogen atoms. Perfluoroakly refers to analkyl group in which all of the constituent hydrogen atoms of the alkylgroup have been replaced with fluorine atoms.

The terms “heterocyclyl” or “heterocyclic group” are art-recognized andrefer to saturated or partially unsaturated 3- to 10-membered ringstructures, alternatively 3- to 7-membered rings, whose ring structuresinclude one to four heteroatoms, such as nitrogen, oxygen, and sulfur.Heterocycles may also be mono-, bi-, or other multi-cyclic ring systems.A heterocycle may be fused to one or more aryl, partially unsaturated,or saturated rings. Heterocyclyl groups include, for example, biotinyl,chromenyl, dihydrofuryl, dihydroindolyl, dihydropyranyl, dihydrothienyl,dithiazolyl, homopiperidinyl, imidazolidinyl, isoquinolyl,isothiazolidinyl, isoxazolidinyl, morpholinyl, oxolanyl, oxazolidinyl,phenoxanthenyl, piperazinyl, piperidinyl, pyranyl, pyrazolidinyl,pyrazolinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolidin-2-onyl,pyrrolinyl, tetrahydrofuryl, tetrahydroisoquinolyl, tetrahydropyranyl,tetrahydroquinolyl, thiazolidinyl, thiolanyl, thiomorpholinyl,thiopyranyl, xanthenyl, lactones, lactams such as azetidinones andpyrrolidinones, sultams, sultones, and the like. The heterocyclic ringmay be substituted at one or more positions with substituents such asalkanoyl, alkoxy, alkyl, alkenyl, alkynyl, amido, amidino, amino, aryl,arylalkyl, azido, carbamate, carbonate, carboxy, cyano, cycloalkyl,ester, ether, formyl, halogen, haloalkyl, heteroaryl, heterocyclyl,hydroxyl, imino, ketone, nitro, phosphate, phosphonato, phosphinato,sulfate, sulfide, sulfonamido, sulfonyl and thiocarbonyl. In certainembodiments, the heterocyclic group is not substituted, i.e., theheterocyclic group is unsubstituted.

The term “heterocyclylalkoxy” as used herein refers to aheterocyclyl-alkyl-O— group.

The term “heterocyclyloxy” refers to a heterocyclyl-O— group.

The term “heterocyclyloxyalkyl” refers to a heterocyclyl-O-alkyl-group.

The terms “hydroxy” and “hydroxyl” as used herein refers to the radical—OH.

The term “oxo” as used herein refers to the radical ═O.

The term “cyano” as used herein refers to the radical CN.

The term “beta amino acid” refers to an amino acid, which have theiramino group bonded to the beta (β) carbon rather than the alpha (“α”)carbon. Non-limiting examples include, without limitation, β-proline andβ-phenylalanine:

“Pharmaceutically or pharmacologically acceptable” include molecularentities and compositions that do not produce an adverse, allergic orother untoward reaction when administered to an animal, or a human, asappropriate. “For human administration, preparations should meetsterility, pyrogenicity, general safety and purity standards as requiredby FDA Office of Biologics standards.

As used in the present disclosure, the term “partial NMDA receptoragonist” is defined as a compound that is capable of binding to aglycine binding site of an NMDA receptor; at low concentrations a NMDAreceptor agonist acts substantially as agonist and at highconcentrations it acts substantially as an antagonist. Theseconcentrations are experimentally determined for each and every “partialagonist.

As used herein “pharmaceutically acceptable carrier” or “excipient”includes any and all solvents, dispersion media, coatings, antibacterialand antifungal agents, isotonic and absorption delaying agents, and thelike that are physiologically compatible. In one embodiment, the carrieris suitable for parenteral administration. Alternatively, the carriercan be suitable for intravenous, intraperitoneal, intramuscular,sublingual or oral administration. Pharmaceutically acceptable carriersinclude sterile aqueous solutions or dispersions and sterile powders forthe extemporaneous preparation of sterile injectable solutions ordispersion. The use of such media and agents for pharmaceutically activesubstances is well known in the art. Except insofar as any conventionalmedia or agent is incompatible with the active compound, use thereof inthe pharmaceutical compositions of the invention is contemplated.Supplementary active compounds can also be incorporated into thecompositions.

The term “pharmaceutically acceptable salt(s)” as used herein refers tosalts of acidic or basic groups that may be present in compounds used inthe present compositions. Compounds included in the present compositionsthat are basic in nature are capable of forming a wide variety of saltswith various inorganic and organic acids. The acids that may be used toprepare pharmaceutically acceptable acid addition salts of such basiccompounds are those that form non-toxic acid addition salts, i.e., saltscontaining pharmacologically acceptable anions, including but notlimited to malate, oxalate, chloride, bromide, iodide, nitrate, sulfate,bisulfate, phosphate, acid phosphate, isonicotinate, acetate, lactate,salicylate, citrate, tartrate, oleate, tannate, pantothenate,bitartrate, ascorbate, succinate, maleate, gentisinate, fumarate,gluconate, glucaronate, saccharate, formate, benzoate, glutamate,methanesulfonate, ethanesulfonate, benzenesulfonate, p-toluenesulfonateand pamoate (i.e., 1,1′-methylene-bis-(2-hydroxy-3-naphthoate)) salts.Compounds included in the present compositions that include an aminomoiety may form pharmaceutically acceptable salts with various aminoacids, in addition to the acids mentioned above. Compounds included inthe present compositions that are acidic in nature are capable offorming base salts with various pharmacologically acceptable cations.Examples of such salts include alkali metal or alkaline earth metalsalts and, particularly, calcium, magnesium, sodium, lithium, zinc,potassium, and iron salts.

The compounds of the disclosure may contain one or more chiral centersand/or double bonds and, therefore, exist as stereoisomers, such asgeometric isomers, enantiomers or diastereomers. The term“stereoisomers” when used herein consist of all geometric isomers,enantiomers or diastereomers. These compounds may be designated by thesymbols “R” or “S,” depending on the configuration of substituentsaround the stereogenic carbon atom. The present invention encompassesvarious stereoisomers of these compounds and mixtures thereof.Stereoisomers include enantiomers and diastereomers. Mixtures ofenantiomers or diastereomers may be designated “(±)” in nomenclature,but the skilled artisan will recognize that a structure may denote achiral center implicitly.

Individual stereoisomers of compounds of the present invention can beprepared synthetically from commercially available starting materialsthat contain asymmetric or stereogenic centers, or by preparation ofracemic mixtures followed by resolution methods well known to those ofordinary skill in the art. These methods of resolution are exemplifiedby (1) attachment of a mixture of enantiomers to a chiral auxiliary,separation of the resulting mixture of diastereomers byrecrystallization or chromatography and liberation of the optically pureproduct from the auxiliary, (2) salt formation employing an opticallyactive resolving agent, or (3) direct separation of the mixture ofoptical enantiomers on chiral chromatographic columns. Stereoisomericmixtures can also be resolved into their component stereoisomers by wellknown methods, such as chiral-phase gas chromatography, chiral-phasehigh performance liquid chromatography, crystallizing the compound as achiral salt complex, or crystallizing the compound in a chiral solvent.Stereoisomers can also be obtained from stereomerically-pureintermediates, reagents, and catalysts by well known asymmetricsynthetic methods.

Geometric isomers can also exist in the compounds of the presentinvention. The symbol

denotes a bond that may be a single, double or triple bond as describedherein. The present invention encompasses the various geometric isomersand mixtures thereof resulting from the arrangement of substituentsaround a carbon-carbon double bond or arrangement of substituents arounda carbocyclic ring. Substituents around a carbon-carbon double bond aredesignated as being in the “Z” or “E” configuration wherein the terms“Z” and “E” are used in accordance with IUPAC standards. Unlessotherwise specified, structures depicting double bonds encompass boththe “E” and “Z” isomers.

Substituents around a carbon-carbon double bond alternatively can bereferred to as “cis” or “trans,” where “cis” represents substituents onthe same side of the double bond and “trans” represents substituents onopposite sides of the double bond. The arrangement of substituentsaround a carbocyclic ring are designated as “cis” or “trans.” The term“cis” represents substituents on the same side of the plane of the ringand the term “trans” represents substituents on opposite sides of theplane of the ring. Mixtures of compounds wherein the substituents aredisposed on both the same and opposite sides of plane of the ring aredesignated “cis/trans.”

The compounds disclosed herein can exist in solvated as well asunsolvated forms with pharmaceutically acceptable solvents such aswater, ethanol, and the like, and it is intended that the inventionembrace both solvated and unsolvated forms. In one embodiment, thecompound is amorphous. In one embodiment, the compound is a polymorph.In another embodiment, the compound is in a crystalline form.

The invention also embraces isotopically labeled compounds of theinvention which are identical to those recited herein, except that oneor more atoms are replaced by an atom having an atomic mass or massnumber different from the atomic mass or mass number usually found innature. Examples of isotopes that can be incorporated into compounds ofthe invention include isotopes of hydrogen, carbon, nitrogen, oxygen,phosphorus, fluorine and chlorine, such as ²H, ³H, ¹³C, ¹⁴C, ¹⁵N, ¹⁸O,¹⁷O, ³¹P, ³²P, ³⁵S, ¹⁸F, and ³⁶Cl, respectively.

Certain isotopically-labeled disclosed compounds (e.g., those labeledwith ³H and ¹⁴C) are useful in compound and/or substrate tissuedistribution assays. Tritiated (i.e., ³H) and carbon-14 (i.e., ¹⁴C)isotopes are particularly preferred for their ease of preparation anddetectability. Further, substitution with heavier isotopes such asdeuterium (i.e., ²H) may afford certain therapeutic advantages resultingfrom greater metabolic stability (e.g., increased in vivo half-life orreduced dosage requirements) and hence may be preferred in somecircumstances. Isotopically labeled compounds of the invention cangenerally be prepared by following procedures analogous to thosedisclosed in the e.g., Examples herein by substituting an isotopicallylabeled reagent for a non-isotopically labeled reagent.

As used in the present disclosure, “NMDA” is defined asN-methyl-d-aspartate.

In the present specification, the term “therapeutically effectiveamount” means the amount of the subject compound that will elicit thebiological or medical response of a tissue, system, animal or human thatis being sought by the researcher, veterinarian, medical doctor or otherclinician. The compounds of the invention are administered intherapeutically effective amounts to treat a disease. Alternatively, atherapeutically effective amount of a compound is the quantity requiredto achieve a desired therapeutic and/or prophylactic effect, such as anamount which results in defined as that amount needed to give maximalenhancement of a behavior (for example, learning), physiologicalresponse (for example, LTP induction), or inhibition of neuropathicpain.

Compounds

Disclosed compounds include those having formula (I):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof (e.g., salts),wherein:

R¹, R², R³, and R⁴ are each independently selected from the groupconsisting of hydrogen; halogen; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;C₂₋₆alkenyl; C₂₋₆alkynyl; C₃₋₆cycloalkyl; phenyl; heteroaryl includingfrom 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; —OR^(x); —C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂;—C(NR^(x))N(R^(x))₂; —OC(O)R^(x); —OCO₂R^(x); —OC(O)N(R^(x))₂;—N(R^(x))₂; —NR^(x)C(O)R^(x); —NR^(x)C(O)N(R^(x))₂; —NR^(x)C(O)OR^(x);and —NR^(x)C(NR^(x))N(R^(x))₂; wherein C₁₋₆alkyl is optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen; hydroxyl; phenyl; heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; and N(R^(x))₂;

R⁵ and R⁶ are independently selected from the group consisting ofhydrogen; C₁-C₆ alkyl, optionally substituted by one, two or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, and N(R^(x))₂; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy,optionally substituted by one, two, or three substituents independentlyselected from the group consisting of halogen, hydroxyl, phenyl, andN(R^(x))₂; and -Q-Ar, wherein Q is a bond or C₁-C₆ alkylene, optionallysubstituted by one, two, or three independently selected halogens, andAr is selected from the group consisting of phenyl and heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S, wherein phenyl and heteroaryl are each optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen, hydroxyl, phenyl, and N(R^(x))₂;or

R⁵ and R⁶, together with the atoms to which they are attached, form aC3-C6 cycloalkyl or heterocyclyl including from 3 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; wherein the C3-C6cycloalkyl and heterocyclyl are each optionally substituted by one, two,or three substituents independently selected from the group consistingof halogen, hydroxyl, phenyl, and N(R^(x))₂;

R⁵⁵ is H, or R⁵⁵ and R⁵, together with the atoms to which they areattached, form a C3-C6 cycloalkyl or heterocyclyl including from 3 to 6ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C1-C3 alkyl), O, and S;wherein the C3-C6 cycloalkyl and heterocyclyl are each optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen, hydroxyl, phenyl, and N(R^(x))₂;

R⁷ and R⁷⁸ are each independently selected from the group consisting ofhydrogen; C₁-C₆ alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy; C₃-C₆cycloalkoxy; heteroaryl including from 5 to 6 ring atoms wherein 1, 2,or 3 of the ring atoms are independently selected from the groupconsisting of N, NH, N(C1-C3 alkyl), O, and S; heterocyclyl includingfrom 3 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; and phenyl; wherein C₁-C₆ alkyl; C₁-C₆ alkoxy; C₃-C₆cycloalkoxy; heteroaryl; heterocyclyl; phenyl are each optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen; hydroxyl; phenyl; heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; and N(R^(x))₂;

R⁸ is selected from the group consisting of hydrogen; halogen; hydroxyl;C₁-C₆ alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy;heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C1-C3 alkyl), O, and S; heterocyclyl including from 3 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom the group consisting of N, NH, N(C1-C3 alkyl), O, and S; andphenyl; wherein C₁-C₆ alkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy;heteroaryl; heterocyclyl; and phenyl are each optionally substituted byone, two, or three substituents independently selected from the groupconsisting of halogen, hydroxyl, phenyl, and N(R^(x))₂; or

R⁷ and R⁸, together with the atoms to which they are attached, formC3-C6 cycloalkyl or heterocyclyl including from 3 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; wherein the C3-C6cycloalkyl and heterocyclyl are each optionally substituted by one, two,or three substituents independently selected from the group consistingof halogen, hydroxyl, phenyl, and N(R^(x))₂;

with the proviso that at least one of R⁷, R⁷⁸, R⁵, and R⁶ is not H;

R⁹ and R¹⁶ are independently selected, for each occurrence, from thegroup consisting of hydrogen; C₁-C₆ alkyl, optionally substituted byone, two, or three substituents substituents independently selected fromthe group consisting of halogen, oxo, hydroxyl, phenyl, and heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; C₁₋₆ perfluoroalkyl; C₂₋₆alkenyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of halogen, oxo, andhydroxyl; C₂₋₆alkynyl, optionally substituted by one, two, or threesubstituents substituents independently selected from the groupconsisting of halogen, oxo, and hydroxyl; C₃₋₆cycloalkyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl, C₁₋₆perfluoroalkyl; halogen, oxo, and hydroxyl; phenyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl; C₁₋₆perfluoroalkyl; C₁₋₆alkoxy; halogen; hydroxyl; —C(O)R^(x); —CO₂(R^(x));—C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂; and —C(R^(x))₃;

or R⁹ and R¹⁰, together with the nitrogen atom to which each isattached, form a heterocyclyl including from 3 to 6 ring atoms, which isoptionally substituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl, C₁₋₆perfluoroalkyl; halogen, oxo, and hydroxyl; wherein when R⁹ and R¹⁶ forma heterocyclyl including 6 ring atoms, the heterocyclyl optionallyincludes, in addition to the nitrogen atom attached to R⁹ and R¹⁰, asecond ring heteroatom selected from the group consisting of N, NH,N(C1-C3 alkyl), O, and S;

R^(x) is independently selected, for each occurrence, from the groupconsisting of hydrogen; halogen; acyl; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;and phenyl; and

R^(y) is hydrogen or C₁₋₃alkyl.

In another aspect, a compound of formula (I) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., one orboth of the proline moieties is/are replaced with a beta-amino acid(s);e.g., the C-terminal and/or the N-terminal is/are replaced with abeta-amino acid(s), and one or both of the proline moieties is/arereplaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (I-A), in which formula (I) is modified suchthat the left-most proline moiety is replaced with:

in which R⁷, R⁸, and R⁷⁸ are as defined anywhere herein. As anotherexample, such compounds can have formula (I-B), in which formula (I) ismodified such that the right-most proline moiety is replaced with:

in which R⁵, R⁶, and R⁵⁵ are as defined anywhere herein. In stillanother embodiment, compounds are provided, in which any one or more ofcompounds of formula (I), (I-A), and (I-B) are modified such that theleft-most (N-terminal) amino acid is replaced with hydrogen, therebyproviding a tripeptide wherein the ring nitrogen of left-most prolinemoiety is bonded to hydrogen.

Embodiments of formula (I), (I-A), and (I-B) tetra- and tripeptidecompounds can include one or more of the following features and/orcombinations of the following features.

In certain embodiments, R¹ is hydrogen, C₁-C₆ alkyl (e.g., methyl), C₁₋₆perfluoroalkyl; or OH.

In certain embodiments, R² is C₁₋₆alkyl, optionally substituted; orphenyl optionally substituted.

In certain embodiments, R¹ is as defined above, and R² is as definedabove. In certain embodiments, R¹ is —OH. In certain embodiments, R² isC₁-C₆ alkyl (e.g., methyl). In certain embodiments, R¹ is —OH, and R² isC₁-C₆ alkyl (e.g., methyl).

In certain embodiments, R³ is —OH. In certain embodiments, R⁴ is C₁-C₆alkyl (e.g., methyl). In certain embodiments, R³ is —OH, and R⁴ is C₁-C₆alkyl (e.g., methyl).

In certain embodiments, R⁵ and/or R⁸ (e.g., R⁸) is independentlyselected from the group consisting of hydroxyl; C₁-C₆ alkoxy (e.g.,methoxy); and C₃-C₆ cycloalkoxy (e.g., cyclopropoxy); wherein C₁-C₆alkoxy and C₃-C₆ cycloalkoxy are each optionally and independentlysubstituted by one, two or three substituents independently selectedfrom the group consisting of halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆perfluoroalkyl; phenyl, and N(R^(x))₂, and the other pyrrolidinesubstituents are hydrogen. In other embodiments, R⁵ and R⁶ or R⁷ and R⁸or R⁵ and R⁵⁵ forms a ring as defined herein.

In certain embodiments, each occurrence of R⁹ and R¹⁰ is hydrogen.

In certain embodiments, R^(x) is hydrogen. In other embodiments, R^(x)is CH₃.

Disclosed compounds include those having formula (II):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof,wherein:

R¹, R², R³, and R⁴ are independently selected from the group consistingof hydrogen; halogen; C₁₋₆alkyl, optionally substituted by one, two, orthree substituents independently selected from the group consisting ofhalogen, hydroxyl, phenyl, heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S, and N(R^(x))₂; C₁₋₆perfluoroalkyl; C₂₋₆alkenyl; C₂₋₆alkynyl; C₃₋₆cycloalkyl; phenyl;heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C1-C3 alkyl), O, and S; —OR^(x); —C(O)R^(x); —CO₂(R^(x));—C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂; —OC(O)R^(x); —OCO₂R^(x);—OC(O)N(R^(x))₂; —N(R^(x))₂; —NR^(x)C(O)R^(x); —NR^(x)C(O)N(R^(x))₂;—NR^(x)C(O)OR^(x); and —NR^(x)C(NR^(x))N(R^(x))₂;

when present, R¹⁵ replaces a hydrogen atom attached to the phenyl ringand, and each occurrence of R¹⁵ is independently selected from the groupconsisting of hydrogen; halogen; hydroxyl; C₁-C₆ alkyl; C₁₋₆perfluoroalkyl; C₁-C₆ alkoxy; heteroaryl including from 5 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom the group consisting of N, NH, N(C1-C3 alkyl), O, and S;heterocyclyl including from 3 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C1-C3 alkyl), O, and S; and phenyl; wherein C₁-C₆ alkyl, C₁-C₆alkoxy, heteroaryl, heterocyclyl, and phenyl are optionally substitutedby one, two, or three substituents independently selected from halogen;hydroxyl; phenyl; heteroaryl including from 5 to 6 ring atoms wherein 1,2, or 3 of the ring atoms are independently selected from the groupconsisting of N, NH, N(C1-C3 alkyl), O, and S; and N(R^(x))₂;

R¹⁶ is selected from the group consisting of hydrogen; halogen;C₁₋₆alkyl; C₁₋₆ perfluoroalkyl; and phenyl;

R¹⁷ and R¹⁸ are each independently selected from the group consisting ofhydrogen; halogen; hydroxyl; C₁-C₆ alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆alkoxy; C₃-C₆ cycloalkoxy; heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; heterocyclylincluding from 3 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; and phenyl; wherein C₁-C₆ alkyl, C₁-C₆ alkoxy, C₃-C₆cycloalkoxy; heteroaryl, heterocyclyl, and phenyl are optionallysubstituted by one, two, or three substituents independently selectedfrom halogen; hydroxyl; phenyl; heteroaryl including from 5 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom the group consisting of N, NH, N(C1-C3 alkyl), O, and S; andN(R^(x))₂; provided that R¹⁷ cannot be halogen or hydroxyl when R¹⁷ is ato the pyrrolidine nitrogen, and R¹⁸ cannot be halogen or hydroxyl whenR¹⁸ is a to the pyrrolidine nitrogen; or

R¹⁷ and R¹⁸, together with the atoms to which they are attached, formC3-C6 cycloalkyl or heterocyclyl including from 3 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; wherein the C3-C6cycloalkyl and heterocyclyl are each optionally substituted by one, two,or three substituents independently selected from the group consistingof halogen, hydroxyl, phenyl, and N(R^(x))₂;

R⁹ and R¹⁰ are independently selected, for each occurrence, from thegroup consisting of hydrogen; C₁-C₆ alkyl, optionally substituted byone, two, or three substituents independently selected from the groupconsisting of halogen, oxo, hydroxyl, phenyl, and heteroaryl includingfrom 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; C₁₋₆ perfluoroalkyl; C₂₋₆alkenyl, optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen, oxo, and hydroxyl; C₂₋₆alkynyl,optionally substituted by one, two, or three substituents independentlyselected from the group consisting of halogen, oxo, and hydroxyl;C₃₋₆cycloalkyl, optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofC₁₋₆alkyl, C₁₋₆ perfluoroalkyl; halogen, oxo, and hydroxyl; phenyl,optionally substituted by one, two, or three substituents independentlyselected from the group consisting of C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;C₁₋₆alkoxy; halogen; hydroxyl; —C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂;—C(NR^(x))N(R^(x))₂; and —C(R^(x))₃;

or R⁹ and R¹⁰, together with the nitrogen atom to which each isattached, form a heterocyclyl including from 3 to 6 ring atoms, which isoptionally substituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl, halogen,oxo, and hydroxyl; wherein when R⁹ and R¹⁰ form a heterocyclyl including6 ring atoms, the heterocyclyl optionally includes, in addition to thenitrogen atom attached to R⁹ and R¹⁰, a second ring heteroatom selectedfrom the group consisting of N, NH, N(C1-C3 alkyl), O, and S;

R^(x) is independently selected, for each occurrence, from the groupconsisting of hydrogen; halogen; acyl; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;and phenyl; and

R^(y) is hydrogen or C₁₋₃alkyl.

In another aspect, a compound of formula (II) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., theproline and/or phenyl alanine moieties is/are replaced with a beta-aminoacid(s); e.g., the C-terminal and/or the N-terminal is/are replaced witha beta-amino acid(s), and the proline and/or phenyl alanine moietiesis/are replaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (II-A), in which formula (II) is modifiedsuch that the proline moiety is replaced with:

in which R¹⁷ and R¹⁸ are as defined anywhere herein. In still anotherembodiment, compounds are provided, in which any one or more ofcompounds of formula (II) and (II-A) are modified such that theleft-most (N-terminal) amino acid is replaced with hydrogen, therebyproviding a tripeptide wherein the ring nitrogen of proline moiety isbonded to hydrogen.

Embodiments of formula (II) and (II-A) tetra- and tripeptide compoundscan include one or more of the following features and/or combinations ofthe following features.

In certain embodiments, R¹ is hydrogen, C₁-C₆ alkyl (e.g., methyl), C₁₋₆perfluoroalkyl; or —OH.

In certain embodiments, R² is C₁₋₆alkyl, optionally substituted; orphenyl optionally substituted.

In certain embodiments, R¹ is as defined above, and R² is as definedabove. In certain embodiments, R¹ is —OH. In certain embodiments, R² isC₁-C₆ alkyl (e.g., methyl). In certain embodiments, R¹ is —OH, and R² isC₁-C₆ alkyl (e.g., methyl).

In certain embodiments, R³ is —OH. In certain embodiments, R⁴ is C₁-C₆alkyl (e.g., methyl). In certain embodiments, R³ is —OH, and R⁴ is C₁-C₆alkyl (e.g., methyl).

In certain embodiments, one of R¹⁷ and R¹⁸ is independently selectedfrom the group consisting of hydroxyl; C₁-C₆ alkoxy (e.g., methoxy); andC₃-C₆ cycloalkoxy (e.g., cyclopropoxy); wherein C₁-C₆ alkoxy and C₃-C₆cycloalkoxy are each optionally and independently substituted by one,two or three substituents independently selected from the groupconsisting of halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl;phenyl, and N(R^(x))₂, and the other is hydrogen. In other embodiments,R¹⁷ and R¹⁸ form a ring.

In certain embodiments, each occurrence of R⁹ and R¹⁰ is hydrogen.

In certain embodiments, R¹⁶ is hydrogen.

In certain embodiments, at least one R¹⁵ is present.

In certain embodiments, R^(x) is hydrogen. In other embodiments, R^(x)is CH₃.

In certain embodiments, R^(y) is hydrogen. In other embodiments, R^(y)is CH₃.

Disclosed compounds include those having formula (III):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof,wherein:

R is —C(R¹)(R¹¹)(R²);

R′ is —C(R³)(R³¹)(R⁴);

each of R¹ and R² is independently selected from the group consistingof:

hydrogen;

halogen;

C₁₋₆alkyl, optionally substituted by one, two or three substituentsindependently selected from the group consisting of halogen; hydroxyl;C₁₋₆alkoxy; phenyl; N(R^(x))₂; C₃-C₆ cycloalkyl; heteroaryl includingfrom 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; and heterocyclyl including from 3 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; wherein the phenyl,cycloakyl, heteroaryl, and heterocyclyl are each optionally substitutedwith one, two, or three substituents that are independently selectedfrom the group consisting of halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆perfluoroalkyl; and N(R^(x))₂;

C₁₋₆ perfluoroalkyl;

C₂₋₆alkenyl;

C₂₋₆alkynyl;

C₃₋₆cycloalkyl optionally substituted by one, two or three independentlyselected C₁₋₃alkyl;

phenyl optionally substituted with one, two, or three substituents thatare independently selected from the group consisting of halogen,hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; and N(R^(x))₂;

heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C1-C3 alkyl), O, and S; which is optionally substituted with one,two, or three substituents independently selected from the groupconsisting of halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; andN(R^(x))₂;

—OR^(x);

—C(O)R^(x);

—CO₂(R^(x));

—C(O)N(R^(x))₂;

—C(NR^(x))N(R^(x))₂;

—OC(O)R^(x);

—OCO₂R^(x);

—OC(O)N(R^(x))₂;

—N(R^(x))₂;

—NR^(x)C(O)R^(x);

—NR^(x)C(O)N(R^(x))₂;

—NR^(x)C(O)OR^(x); and

—NR^(x)C(NR^(x))N(R^(x))₂; or

R¹ and R² together with the carbon atom to which each is attached form aring selected from the group consisting of (i) phenyl and (ii)heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from N, NH, N(C₁-C₃ alkyl), O, andS; each of which is optionally substituted with one, two, or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, andN(R^(x))₂;

each of R³ and R⁴ is independently selected from the group consistingof:

hydrogen;

halogen;

C₁₋₆alkyl, optionally substituted with one, two or three substituentsindependently selected from the group consisting of halogen; hydroxyl;C₁₋₆alkoxy; phenyl; N(R^(x))₂; C₃-C₆ cycloalkyl; heteroaryl includingfrom 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C₁-C₃alkyl), O, and S; and heterocyclyl including from 3 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C₁-C₃ alkyl), O, and S; wherein the phenyl,cycloakyl, heteroaryl, and heterocyclyl are each optionally substitutedwith one, two, or three substituents independently selected from thegroup consisting of halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl;and N(R^(x))₂;

C₁₋₆ perfluoroalkyl;

C₂₋₆alkenyl;

C₂₋₆alkynyl;

C₃₋₆cycloalkyl optionally substituted with one, two or threeindependently selected C₁₋₃alkyl;

phenyl optionally substituted with one, two, or three substituents thatare independently selected from the group consisting of halogen,hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; and N(R^(x))₂;

heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C₁-C₃ alkyl), O, and S; which is optionally substituted with one,two, or three substituents independently selected from the groupconsisting of halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; andN(R^(x))₂,

—OR^(x);

—C(O)R^(x);

—CO₂(R^(x));

—C(O)N(R^(x))₂;

—C(NR^(x))N(R^(x))₂;

—OC(O)R^(x);

—OCO₂R^(x);

—OC(O)N(R^(x))₂;

—N(R^(x))₂;

—NR^(x)C(O)R^(x);

—NR^(x)C(O)N(R^(x))₂;

—NR^(x)C(O)OR^(x); and

—NR^(x)C(NR^(x))N(R^(x))₂; or

R³ and R⁴ together with the carbon atom to which each is attached form aring selected from the group consisting of (i) phenyl and (ii)heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from N, NH, N(C₁-C₃ alkyl), O, andS; each of which is optionally substituted with one, two, or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, andN(R^(x))₂;

each of R¹¹ and R³¹ is, independently, hydrogen, C₁-C₆ alkyl, or C₁₋₆perfluoroalkyl; or

R¹¹ is absent when R¹ and R² together form phenyl or heteroaryl;

R³¹ is absent when R³ and R⁴ together form phenyl or heteroaryl;

each of R^(a), R^(h), R^(e), and R^(d) is independently selected fromthe group consisting of hydrogen; halogen; hydroxyl; C₁-C₆ alkyl; C₁₋₆perfluoroalkyl; C₁-C₆ alkoxy; heteroaryl including from 5 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom the group consisting of N, NH, N(C₁-C₃ alkyl), O, and S;heterocyclyl including from 3 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C₁-C₃ alkyl), O, and S; and phenyl; wherein C₁-C₆ alkyl, C₁-C₆alkoxy, heteroaryl, heterocyclyl, and phenyl are each optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen, hydroxyl, phenyl, and N(R^(x))₂;

each of R^(e) and R^(g) is independently selected from the groupconsisting of hydrogen; acyl; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl; andphenyl;

R^(f) is selected from the group consisting of hydrogen; halogen; acyl;C₁₋₆alkyl; C₁₋₆ perfluoroalkyl; and phenyl;

R^(h) is hydrogen or C₁₋₃alkyl;

R^(i) is selected from the group consisting of hydrogen; halogen; cyano,CH₃, and CF₃;

R²¹ is selected from the group consisting of hydrogen; C₁-C₆ alkyl; C₁₋₆perfluoroalkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy; C₂-C₆ acyloxy,heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C₁-C₃ alkyl), O, and S; heterocyclyl including from 3 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom the group consisting of N, NH, N(C₁-C₃ alkyl), O, and S; andphenyl; wherein C₁-C₆ alkyl, C₁-C₆ alkoxy, C₃-C₆ cycloalkoxy,heteroaryl, heterocyclyl, and phenyl are each optionally andindependently substituted by one, two or three substituents that areindependently selected from the group consisting of halogen, hydroxyl,C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl, phenyl, and N(R^(x))₂;

each of R²² and R²³ is independently selected from the group consistingof hydrogen; halogen; hydroxyl; C₁-C₆ alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆alkoxy; C₃-C₆ cycloalkoxy; C₂-C₆ acyloxy, heteroaryl including from 5 to6 ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C₁-C₃ alkyl), O, and S;heterocyclyl including from 3 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C₁-C₃ alkyl), O, and S; and phenyl; wherein C₁-C₆ alkyl, C₁-C₆alkoxy, C₃-C₆ cycloalkoxy, heteroaryl, heterocyclyl, and phenyl are eachoptionally and independently substituted by one, two or threesubstituents that are independently selected from the group consistingof halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, andN(R^(x))₂; or

R²¹ and R²², together with the carbon atoms to which each is attached,form a ring selected from the group consisting of (i) 3-6 memberedheterocyclyl wherein 1, 2, or 3 of the ring atoms are independentlyselected from N, NH, N(C₁-C₃ alkyl), O, and S; (ii) C₃-C₆ cycloalkyl;(iii) phenyl; and (iv) heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from N,NH, N(C₁-C₃ alkyl), O, and S; wherein each of (i)-(iv) is optionallysubstituted by one, two, or three substituents that are independentlyselected from the group consisting of halogen, hydroxyl, C₁-C₆ alkyl,C₁₋₆ perfluoroalkyl; phenyl, and N(R^(x))₂; and R²³ is as defined above;or

R²² and R²³, together with the carbon atoms to which each is attached,form a ring selected from the group consisting of (i) 3-6 memberedheterocyclyl wherein 1, 2, or 3 of the ring atoms are independentlyselected from N, NH, N(C₁-C₃ alkyl), O, and S; (ii) C₃-C₆ cycloalkyl;(iii) phenyl; and (iv) heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from N,NH, N(C₁-C₃ alkyl), O, and S; wherein each of (i)-(iv) is optionallysubstituted by one, two, or three substituents that are independentlyselected from the group consisting of halogen, hydroxyl, C₁-C₆ alkyl,C₁₋₆ perfluoroalkyl; phenyl, and N(R^(x))₂; and R²¹ is as defined above;

each occurrence of R⁹ and R¹⁰ is independently selected from the groupconsisting of hydrogen; C₁-C₆ alkyl, optionally substituted by one, two,or three substituents each independently selected from the groupconsisting of halogen, oxo, and hydroxyl; C₁₋₆ perfluoroalkyl;C₂₋₆alkenyl, optionally substituted by one, two, or three substituentseach independently selected from the group consisting of halogen, oxo,and hydroxyl; C₂₋₆alkynyl, optionally substituted by one, two, or threesubstituents each independently selected from the group consisting ofhalogen, oxo, and hydroxyl; C₃₋₆cycloalkyl, optionally substituted byone, two, or three substituents each independently selected from thegroup consisting of C₁₋₆alkyl, C₁₋₆ perfluoroalkyl; halogen, oxo, andhydroxyl; and phenyl, optionally substituted by one, two, or threesubstituents each independently selected from the group consisting ofC₁₋₆alkyl; C₁₋₆ perfluoroalkyl; C₁₋₆alkoxy; halogen; hydroxyl;—C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂; and—C(R^(x))₃;

or R⁹ and R¹⁰, together with the nitrogen atom to which each isattached, form heterocyclyl including from 3 to 6 ring atoms wherein 1,2, or 3 of the ring atoms are independently selected from the groupconsisting of N, NH, N(C1-C3 alkyl), O, and S; which is optionallysubstituted by one, two, or three substituents each independentlyselected from the group consisting of C₁₋₆alkyl, C₁₋₆ perfluoroalkyl;halogen, oxo, and hydroxyl; wherein when R⁹ and R¹⁰ form a heterocyclylincluding 6 ring atoms, the heterocyclyl optionally includes, inaddition to the nitrogen atom attached to R⁹ and R¹⁰, a second ringheteroatom selected from the group consisting of N, NH, N(C1-C3 alkyl),O, and S; and

R^(x) is independently selected, for each occurrence, from the groupconsisting of hydrogen; halogen; acyl; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;and phenyl.

In another aspect, a compound of formula (III) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., theproline and/or trytophan moieties is/are replaced with a beta-aminoacid(s); e.g., the C-terminal and/or the N-terminal is/are replaced witha beta-amino acid(s), and the proline and/or tryptophan moieties is/arereplaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (III-A), in which formula (III) is modifiedsuch that the proline moiety is replaced with:

in which R²¹, R²², and R²³ are as defined anywhere herein. In stillanother embodiment, compounds are provided, in which any one or more ofcompounds of formula (III) and (III-A) are modified such that theleft-most (N-terminal) amino acid is replaced with hydrogen, therebyproviding a tripeptide wherein the ring nitrogen of proline moiety isbonded to hydrogen.

Embodiments of formula (III) and (III-A) tetra- and tripeptide compoundscan include one or more of the following features and/or combinations ofthe following features.

In certain embodiments, R²¹ and R²² and R²² and R²³ do not form a ringas defined herein.

For example, one of R²² and R²³ (e.g., R²²) is selected from the groupconsisting of halogen; hydroxyl; C₁-C₆ alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆alkoxy; C₃-C₆ cycloalkoxy; C₂-C₆ acyloxy, heteroaryl including from 5 to6 ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C₁-C₃ alkyl), O, and S;heterocyclyl including from 3 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C₁-C₃ alkyl), O, and S; and phenyl; wherein C₁-C₆ alkyl, C₁-C₆alkoxy, C₃-C₆ cycloalkoxy, heteroaryl, heterocyclyl, and phenyl are eachoptionally and independently substituted by one, two or threesubstituents that are independently selected from the group consistingof halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, andN(R^(x))₂, and the other is hydrogen.

As another example, one of R²² and R²³ (e.g., R²²) is independentlyselected from the group consisting of hydroxyl; C₁-C₆ alkoxy (e.g.,methoxy); and C₃-C₆ cycloalkoxy (e.g., cyclopropoxy); C₂-C₆ acyloxy(—OC(O)CH₃), wherein C₁-C₆ alkoxy and C₃-C₆ cycloalkoxy are eachoptionally and independently substituted by one, two or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, andN(R^(x))₂, and the other is hydrogen.

In certain of these embodiments, R²¹ is hydrogen.

In other embodiments, R²¹ and R²² (together with the carbon atoms towhich each is attached) or R²² and R²³ (together with the carbon atomsto which each is attached) do form a ring as defined herein.

In certain embodiments, R²¹ and R²² form a ring as defined herein; e.g.,a C₃-C₆ cycloalkyl ring (e.g., a C₃ or C₅), which is optionallysubstituted by one, two, or three substituents that are independentlyselected from the group consisting of halogen, hydroxyl, C₁-C₆ alkyl,C₁₋₆ perfluoroalkyl; phenyl, and N(R^(x))₂; or a phenyl ring, which isoptionally substituted by one, two, or three substituents that areindependently selected from the group consisting of halogen, hydroxyl,C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, and N(R^(x))₂; or a heteroarylring including from 5 to 6 ring atoms wherein 1, 2, or 3 of the ringatoms are independently selected from N, NH, N(C₁-C₃ alkyl), O, and S;each of which is optionally substituted by one, two, or threesubstituents that are independently selected from the group consistingof halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, andN(R^(x))₂.

In certain of these embodiments, R²³ is hydrogen.

In certain embodiments (e.g., when the proline is an α-proline), R²² andR²³ form a ring as defined herein; e.g., a C₃-C₆ cycloalkyl ring (e.g.,a C₃ or C₅), which is optionally substituted by one, two, or threesubstituents that are independently selected from the group consistingof halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; phenyl, andN(R^(x))₂; or a phenyl ring, which is optionally substituted by one,two, or three substituents that are independently selected from thegroup consisting of halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl;phenyl, and N(R^(x))₂; or a heteroaryl ring including from 5 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom N, NH, N(C₁-C₃ alkyl), O, and S; each of which is optionallysubstituted by one, two, or three substituents that are independentlyselected from the group consisting of halogen, hydroxyl, C₁-C₆ alkyl,C₁₋₆ perfluoroalkyl; phenyl, and N(R^(x))₂.

In certain of these embodiments, R²¹ is hydrogen.

In certain embodiments, R¹ and R² do not form a ring as defined herein.

In certain embodiments, R¹ is hydrogen, C₁-C₆ alkyl (e.g., methyl), C₁₋₆perfluoroalkyl; or —OH (e.g., hydrogen, C₁-C₆ alkyl (e.g., methyl), or—OH).

In certain embodiments, R² is: C₁₋₆alkyl, optionally substituted by one,two or three substituents that are independently selected from the groupconsisting of halogen, hydroxyl, C₁₋₆alkoxy, phenyl, N(R^(x))₂, C₃-C₆cycloalkyl, heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or3 of the ring atoms are independently selected from the group consistingof N, NH, N(C1-C3 alkyl), O, and S, and heterocyclyl including from 3 to6 ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C1-C3 alkyl), O, and S;wherein the phenyl, cycloakyl, heteroaryl, and heterocyclyl are eachoptionally substituted with one, two, or three substituents that areindependently selected from the group consisting of halogen, hydroxyl,C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; and N(R^(x))₂; C₁₋₄perhaloalkyl (e.g.,CF₃); or phenyl optionally substituted with one, two, or threesubstituents that are independently selected from the group consistingof halogen, hydroxyl, C₁-C₆ alkyl, C₁₋₆ perfluoroalkyl; and N(R^(x))₂.In certain embodiments, R² is unsubstituted C₁₋₆alkyl or substituted C₁or C₂ (e.g., C₁) alkyl.

In certain embodiments, R¹ is as defined above, and R² is as definedabove in the two preceding paragraphs. In certain embodiments, R¹ is—OH, and R² is as defined above . In certain embodiments, R¹ ishydrogen, and R² is as defined above. In certain embodiments, R¹ isC₁-C₆ alkyl (e.g., methyl), and R² is as defined above.

In certain embodiments, R¹¹ is hydrogen. In other embodiments, R¹¹ isC₁-C₆ alkyl (e.g., methyl); e.g., when R¹ and R² are also C₁-C₆ alkyl(e.g., methyl).

In other embodiments, R¹ and R² together with the carbon atoms to whicheach is attached form a ring as defined herein (e.g., a phenyl ring);and R¹¹ is absent.

In certain embodiments, R³ is —OH. In certain embodiments, R⁴ is C₁-C₆alkyl (e.g., methyl). In certain embodiments, R³ is —OH, and R⁴ is C₁-C₆alkyl (e.g., methyl). In certain embodiments, R³¹ is hydrogen. Incertain embodiments, R³ is —OH, R⁴ is C₁-C₆ alkyl (e.g., methyl), andR³¹ is hydrogen.

In certain embodiments, each of R^(a), R^(b), R^(c), R^(d), R^(e), andR^(f) is hydrogen.

In certain embodiments, each occurrence of R⁹ and R¹⁰ is hydrogen.

In certain embodiments, R^(i) is hydrogen.

In certain embodiments, each of R^(a), R^(b), R^(c), R^(d), R^(e),R^(f), R^(i), R⁹ and R¹⁰ is hydrogen.

In certain embodiments, R^(g) is hydrogen. In other embodiments, R^(g)is CH₃.

In certain embodiments, R^(h) is hydrogen. In other embodiments, R^(h)is CH₃.

In certain embodiments, R¹ is —OH, and R² is as defined above (e.g., R²is C₁-C₆ alkyl (e.g., methyl)), or R¹ is hydrogen, and R² is as definedabove, or R¹ is C₁-C₆ alkyl (e.g., methyl), and R² is as defined above,(e.g., R¹ is —OH, and R² is as defined above, e.g., R² is C₁-C₆ alkyl(e.g., methyl)); R¹¹ is hydrogen; R²¹, R²² and R²³ are hydrogen, or R²¹and R²³ are hydrogen, and R²² is other than hydrogen as defined herein(e.g., hydroxyl; C₁-C₆ alkoxy (e.g., methoxy); and C₃-C₆ cycloalkoxy(e.g., cyclopropoxy); C₂-C₆ acyloxy (—OC(O)CH₃)); R³ is —OH, R⁴ is C₁-C₆alkyl (e.g., methyl), R³¹ is hydrogen; each of R^(a), R^(b), R^(e),R^(d), R^(e), R^(f), R^(i), R⁹ and R¹⁰ is hydrogen; R^(g) is hydrogen orCH₃; and R^(g) is hydrogen or CH₃. In certain of these embodiments, theproline is an α-proline. In other of these embodiments, the proline isan β-proline.

Non-limiting exemplary compounds include those delineated in Table 1,FIG. 1, and FIG. 2.

Disclosed compounds include those having formula (IV):

and pharmaceutically acceptable salts, stereoisomers, metabolites, andhydrates thereof (e.g., salts),

wherein:

R is selected from the group consisting of C₁₋₆alkyl; C₁₋₆perfluoroalkyl; C₃₋₆cycloalkyl; phenyl; heteroaryl including from 5 to 6ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C1-C3 alkyl), O, and S;—OR^(x); —C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂;—OC(O)R^(x); —OCO₂R^(x); —OC(O)N(R^(x))₂; —N(R^(x))₂; —NR^(x)C(O)R^(x);—NR^(x)C(O)N(R^(x))₂; —NR^(x)C(O)OR^(x); and —NR^(x)C(NR^(x))N(R^(x))₂;wherein C₁₋₆alkyl is optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, phenyl, heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; and N(R^(x))₂;

R⁵ and R⁶ are independently selected from the group consisting ofhydrogen; C₁-C₆ alkyl, optionally substituted by one, two or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, and N(R^(x))₂; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy,optionally substituted by one, two, or three substituents independentlyselected from the group consisting of halogen, hydroxyl, phenyl, andN(R^(x))₂; and -Q-Ar, wherein Q is a bond or C₁-C₆ alkylene, optionallysubstituted by one, two, or three independently selected halogens, andAr is selected from the group consisting of phenyl and heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S, wherein phenyl and heteroaryl are each optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen, hydroxyl, phenyl, and N(R^(x))₂;or

R⁵ and R⁶, together with the atoms to which they are attached, form aC3-C6 cycloalkyl or heterocyclyl including from 3 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; wherein the C3-C6cycloalkyl and heterocyclyl are each optionally substituted by one, two,or three substituents independently selected from the group consistingof halogen, hydroxyl, phenyl, and N(R^(x))₂;

R⁵⁵ is H, or R⁵⁵ and R⁵, together with the atoms to which they areattached, form a C3-C6 cycloalkyl or heterocyclyl including from 3 to 6ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C1-C3 alkyl), O, and S;wherein the C3-C6 cycloalkyl and heterocyclyl are each optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen, hydroxyl, phenyl, and N(R^(x))₂;

R⁷ and R⁷⁸ are each independently selected from the group consisting ofhydrogen; C₁-C₆ alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy; C₃-C₆cycloalkoxy; heteroaryl including from 5 to 6 ring atoms wherein 1, 2,or 3 of the ring atoms are independently selected from the groupconsisting of N, NH, N(C1-C3 alkyl), O, and S; heterocyclyl includingfrom 3 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; and phenyl; wherein C₁-C₆ alkyl; C₁-C₆ alkoxy; C₃-C₆cycloalkoxy; heteroaryl; heterocyclyl; phenyl are each optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen, hydroxyl, phenyl, heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S, and N(R^(x))₂;

R⁸ is selected from the group consisting of hydrogen; halogen; hydroxyl;C₁-C₆ alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy;heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C1-C3 alkyl), O, and S; heterocyclyl including from 3 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom the group consisting of N, NH, N(C1-C3 alkyl), O, and S; andphenyl; wherein C₁-C₆ alkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy;heteroaryl; heterocyclyl; and phenyl are each optionally substituted byone, two, or three substituents independently selected from the groupconsisting of halogen, hydroxyl, phenyl, and N(R^(x))₂; or

R⁷ and R⁸, together with the atoms to which they are attached, formC3-C6 cycloalkyl or heterocyclyl including from 3 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; wherein the C3-C6cycloalkyl and heterocyclyl are each optionally substituted by one, two,or three substituents independently selected from the group consistingof halogen, hydroxyl, phenyl, and N(R^(x))₂;

R⁹ and R¹⁰ are independently selected, for each occurrence, from thegroup consisting of hydrogen; C₁-C₆ alkyl, optionally substituted byone, two, or three substituents substituents independently selected fromthe group consisting of halogen, oxo, hydroxyl, phenyl, and heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; C₁₋₆ perfluoroalkyl; C₂₋₆alkenyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of halogen, oxo, andhydroxyl; C₂₋₆alkynyl, optionally substituted by one, two, or threesubstituents substituents independently selected from the groupconsisting of halogen, oxo, and hydroxyl; C₃₋₆cycloalkyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl, C₁₋₆perfluoroalkyl; halogen, oxo, and hydroxyl; phenyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl; C₁₋₆perfluoroalkyl; C₁₋₆alkoxy; halogen; hydroxyl; —C(O)R^(x); —CO₂(R^(x));—C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂; and —C(R^(x))₃;

or R⁹ and R¹⁰, together with the nitrogen atom to which each isattached, form a heterocyclyl including from 3 to 6 ring atoms, which isoptionally substituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl, halogen,oxo, and hydroxyl; wherein when R⁹ and R¹⁰ form a heterocyclyl including6 ring atoms, the heterocyclyl optionally includes, in addition to thenitrogen atom attached to R⁹ and R¹⁰, a second ring heteroatom selectedfrom the group consisting of N, NH, N(C1-C3 alkyl), O, and S;

R^(x) is independently selected, for each occurrence, from the groupconsisting of hydrogen; halogen; acyl; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;and phenyl; and

R^(y) is C₁₋₃alkyl.

In another aspect, a compound of formula (IV) is provided, in which oneor more (e.g., one, two, three, or four) of the four constituent aminoacids is replaced with a beta-amino acid (e.g., the C-terminal and/orthe N-terminal is/are replaced with a beta-amino acid(s); e.g., one orboth of the proline moieties is/are replaced with a beta-amino acid(s);e.g., the C-terminal and/or the N-terminal is/are replaced with abeta-amino acid(s), and one or both of the proline moieties is/arereplaced with a beta-amino acid(s)). In some embodiments, theconstituent amino acid is replaced with its corresponding beta-aminoacid (e.g., proline replaced with beta-proline). By way of example, suchcompounds can have formula (IV-A), in which formula (IV) is modifiedsuch that the left-most proline moiety is replaced with:

in which R⁷, R⁸, and R⁷⁸ are as defined anywhere herein. As anotherexample, such compounds can have formula (IV-B), in which formula (IV)is modified such that the right-most proline moiety is replaced with:

in which R⁵, R⁶, and R⁵⁵ are as defined anywhere herein. In stillanother embodiment, compounds are provided, in which any one or more ofcompounds of formula (IV), (IV-A), and (IV-B) are modified such that theleft-most (N-terminal) amino acid is replaced with hydrogen, therebyproviding a tripeptide wherein the ring nitrogen of left-most prolinemoiety is bonded to hydrogen.

Embodiments of formula (IV), (IV-A), and (IV-B) tetra- and tripeptidecompounds can include one or more of the following features and/orcombinations of the following features.

In certain embodiments, R is C₁₋₆alkyl (e.g., isopropyl).

In certain embodiments, R^(y) is CH₃.

In certain embodiments, R³ is —OH. In certain embodiments, R⁴ is C₁-C₆alkyl (e.g., methyl). In certain embodiments, R³ is —OH, and R⁴ is C₁-C₆alkyl (e.g., methyl).

In certain embodiments, R⁵, R⁶, R⁷, R⁸, R⁵⁵, and R⁷⁸ are each hydrogen.In other embodiments, R⁵ and R⁶ or R⁷ and R⁸ or R⁵ and R⁵⁵ forms a ringas defined herein, and the other pyrrolidine substituents are hydrogen.

A non-limiting exemplary compound is delineated in FIG. 4.

Disclosed compounds include those having formula (V):T¹-P¹-P²-T²   (V)or a pharmaceutically acceptable salt thereof,wherein:

T¹ is hydrogen or has formula (A):

P¹ has formula (B) or formula (C):

P² has formula (D) or formula (E):

T² has formula (F):

wherein: any line intersected by

* represents the single bond connecting the carbonyl carbon of T¹ andthe nitrogen atom of formula (B) or formula (C) in P¹; any lineintersected by

# represents the single bond connecting the carbonyl carbon of formula(B) or formula (C) in P¹ and the nitrogen atom of formula (D) or formula(E) in P²; and any line intersected by

+ represents the single bond connecting the carbonyl carbon of formula(D) or formula (E) in P² and the nitrogen atom of T²;

R¹, R², R³, and R⁴ are each independently selected from the groupconsisting of hydrogen; halogen; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;C₂₋₆alkenyl; C₂₋₆alkynyl; C₃₋₆cycloalkyl; phenyl; heteroaryl includingfrom 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; —OR^(x); —C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂;—C(NR^(x))N(R^(x))₂; —OC(O)R^(x); —OCO₂R^(x); —OC(O)N(R^(x))₂;—N(R^(x))₂; —NR^(x)C(O)R^(x); —NR^(x)C(O)N(R^(x))₂; —NR^(x)C(O)OR^(x);and —NR^(x)C(NR^(x))N(R^(x))₂; wherein C₁₋₆alkyl is optionallysubstituted by one, two, or three substituents independently selectedfrom the group consisting of halogen; hydroxyl; phenyl; heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; and N(R^(x))₂;

R⁹ and R¹⁰ are independently selected, for each occurrence, from thegroup consisting of hydrogen; C₁-C₆ alkyl, optionally substituted byone, two, or three substituents substituents independently selected fromthe group consisting of halogen, oxo, hydroxyl, phenyl, and heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; C₁₋₆ perfluoroalkyl; C₂₋₆alkenyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of halogen, oxo, andhydroxyl; C₂₋₆alkynyl, optionally substituted by one, two, or threesubstituents substituents independently selected from the groupconsisting of halogen, oxo, and hydroxyl; C₃₋₆cycloalkyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl, C₁₋₆perfluoroalkyl; halogen, oxo, and hydroxyl; phenyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl; C₁₋₆perfluoroalkyl; C₁₋₆alkoxy; halogen; hydroxyl; —C(O)R^(x); —CO₂(R^(x));—C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂; and —C(R^(x))₃;

or R⁹ and R¹⁰, together with the nitrogen atom to which each isattached, form a heterocyclyl including from 3 to 6 ring atoms, which isoptionally substituted by one, two, or three substituents substituentsindependently selected from the group consisting of C₁₋₆alkyl, C₁₋₆perfluoroalkyl; halogen, oxo, and hydroxyl; wherein when R⁹ and R¹⁰ forma heterocyclyl including 6 ring atoms, the heterocyclyl optionallyincludes, in addition to the nitrogen atom attached to R⁹ and R¹⁰, asecond ring heteroatom selected from the group consisting of N, NH,N(C1-C3 alkyl), O, and S;

R^(x) is independently selected, for each occurrence, from the groupconsisting of hydrogen; halogen; acyl; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl;and phenyl; and

R^(y) is hydrogen or C₁₋₃alkyl. In some embodiments, it is provided thatthe compound is not GLYX-13.

In some embodiments, T¹ has formula (A). In other embodiments, T¹ ishydrogen. Embodiments in which T¹ has formula (A) or T¹ is hydrogen caninclude one or more of the following features and/or combinations of thefollowing features.

P¹ can have formula (C). P² can have formula (D). In certainembodiments, C₃ in formula (C) has the R-configuration. In otherembodiments, C₃ in formula (C) has the 5-configuration. In certainembodiments, C₂ in formula (D) has the R-configuration. In otherembodiments, C₂ in formula (D) has the S-configuration.

In certain embodiments, P¹ can have formula (C), and P² can have formula(D). For example, C₃ in formula (C) can have the R-configuration, and C₂in formula (D) can have the R-configuration; or C₃ in formula (C) canhave the R-configuration, and C₂ in formula (D) can have theS-configuration. As another example, C₃ in formula (C) can have theS-configuration, and C₂ in formula (D) can have the R-configuration; orC₃ in formula (C) can have the 5-configuration, and C₂ in formula (D)can have the S-configuration.

P¹ can have formula (B). P² can have formula (E). In certainembodiments, C₃ in formula (E) has the R-configuration. In otherembodiments, C₃ in formula (E) has the S-configuration. In certainembodiments, C₂ in formula (B) has the R-configuration. In otherembodiments, C₂ in formula (B) has the S-configuration.

In certain embodiments, P¹ can have formula (B), and P² can have formula(E). For example, C₃ in formula (E) can have the R-configuration, and C₂in formula (B) can have the R-configuration; or C₃ in formula (E) canhave the R-configuration, and C₂ in formula (B) can have theS-configuration. As another example, C₃ in formula (E) can have theS-configuration, and C₂ in formula (B) can have the R-configuration; orC₃ in formula (E) can have the 5-configuration, and C₂ in formula (B)can have the S-configuration.

In still other embodiments, P¹ has formula (B), P² has formula (D), andC₂ in either (or both) formula (B) or formula (D) has theR-configuration.

R^(y) can be H.

R¹ can be —OR^(x). In certain embodiments, R^(x) is hydrogen orC₁₋₆alkyl. In certain embodiments, R^(x) is hydrogen (i.e., R¹ is —OH).

R² can be C₁-C₆ alkyl optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen; hydroxyl; phenyl; heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; and N(R^(x))₂. Incertain embodiments, R² is C₁-C₆ alkyl (e.g., CH₃).

R¹ can be —OR^(x). In certain embodiments, R^(x) is hydrogen orC₁₋₆alkyl. In certain embodiments, R^(x) is hydrogen (i.e., R¹ is —OH).

R² can be C₁-C₆ alkyl optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen; hydroxyl; phenyl; heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; and N(R^(x))₂. Incertain embodiments, R² is C₁-C₆ alkyl (e.g., CH₃).

R³ can be —OR^(x). In certain embodiments, R^(x) is hydrogen orC₁₋₆alkyl. In certain embodiments, R^(x) is hydrogen (i.e., R³ is —OH).

R⁴ can be C₁-C₆ alkyl optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen; hydroxyl; phenyl; heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; and N(R^(x))₂. Incertain embodiments, R⁴ is C₁-C₆ alkyl (e.g., CH₃).

Each occurrence of R⁹ and R¹⁰ can be hydrogen.

The compounds of the present disclosure and formulations thereof mayhave a plurality of chiral centers. Each chiral center may beindependently R, S, or any mixture of R and S. For example, in someembodiments, a chiral center may have an R:S ratio of between about100:0 and about 50:50, between about 100:0 and about 75:25, betweenabout 100:0 and about 85:15, between about 100:0 and about 90:10,between about 100:0 and about 95:5, between about 100:0 and about 98:2,between about 100:0 and about 99:1, between about 0:100 and 50:50,between about 0:100 and about 25:75, between about 0:100 and about15:85, between about 0:100 and about 10:90, between about 0:100 andabout 5:95, between about 0:100 and about 2:98, between about 0:100 andabout 1:99, between about 75:25 and 25:75, and about 50:50. Formulationsof the disclosed compounds comprising a greater ratio of one or moreisomers (i.e., R and/or S) may possess enhanced therapeuticcharacteristic relative to racemic formulations of a disclosed compoundsor mixture of compounds.

Disclosed compounds may provide for efficient cation channel opening atthe NMDA receptor, e.g. may bind or associate with the glutamate site ofthe NMDA receptor to assist in opening the cation channel. The disclosedcompounds may be used to regulate (turn on or turn off) the NMDAreceptor through action as an agonist.

The compounds as described herein may be glycine site NMDA receptorpartial agonists. A partial agonist as used in this context will beunderstood to mean that at a low concentration, the analog acts as anagonist and at a high concentration, the analog acts as an antagonist.Glycine binding is not inhibited by glutamate or by competitiveinhibitors of glutamate, and also does not bind at the same site asglutamate on the NMDA receptor. A second and separate binding site forglycine exists at the NMDA receptor. The ligand-gated ion channel of theNMDA receptor is, thus, under the control of at least these two distinctallosteric sites. Disclosed compounds may be capable of binding orassociating with the glycine binding site of the NMDA receptor. In someembodiments, disclosed compounds may possess a potency that is 10-foldor greater than the activity of existing NMDA receptor glycine sitepartial agonists. For example, disclosed compounds may possess a 10-foldto 20-fold enhanced potency compared to GLYX-13. GLYX-13 is representedby:

For example, provided herein are compounds that may be at least about20-fold more potent as compared to GLYX-13, as measured by burstactivated NMDA receptor-gated single neuron conductance (I_(NMDA)) in aculture of hippocampal CA1 pyramidal neurons at a concentration of 50nM. In another embodiment, a provided compound may be capable ofgenerating an enhanced single shock evoked NMDA receptor-gated singleneuron conductance (I_(NMDA)) in hippocampal CA1 pyramidal neurons atconcentrations of 100 nM to 1 μM. Disclosed compounds may have enhancedpotency as compared to GLYX-13 as measured by magnitude of long termpotentiation (LTP) at Schaffer collateral-CA-1 synapses in in vitrohippocampal slices.

The disclosed compounds may exhibit a high therapeutic index. Thetherapeutic index, as used herein, refers to the ratio of the dose thatproduces a toxicity in 50% of the population (i.e., TD₅₀) to the minimumeffective dose for 50% of the population (i.e., ED₅₀) Thus, thetherapeutic index=(TD₅₀):(ED₅₀). In some embodiments, a disclosedcompound may have a therapeutic index of at least about 10:1, at leastabout 50:1, at least about 100:1, at least about 200:1, at least about500:1, or at least about 1000:1.

Compositions

In other aspects, formulations and compositions comprising the disclosedcompounds and optionally a pharmaceutically acceptable excipient areprovided. In some embodiments, a contemplated formulation comprises aracemic mixture of one or more of the disclosed compounds.

Contemplated formulations may be prepared in any of a variety of formsfor use. By way of example, and not limitation, the compounds may beprepared in a formulation suitable for oral administration, subcutaneousinjection, or other methods for administering an active agent to ananimal known in the pharmaceutical arts.

Amounts of a disclosed compound as described herein in a formulation mayvary according to factors such as the disease state, age, sex, andweight of the individual. Dosage regimens may be adjusted to provide theoptimum therapeutic response. For example, a single bolus may beadministered, several divided doses may be administered over time or thedose may be proportionally reduced or increased as indicated by theexigencies of the therapeutic situation. It is especially advantageousto formulate parenteral compositions in dosage unit form for ease ofadministration and uniformity of dosage. Dosage unit form as used hereinrefers to physically discrete units suited as unitary dosages for themammalian subjects to be treated; each unit containing a predeterminedquantity of active compound calculated to produce the desiredtherapeutic effect in association with the required pharmaceuticalcarrier.

The specification for the dosage unit forms of the invention aredictated by and directly dependent on (a) the unique characteristics ofthe compound selected and the particular therapeutic effect to beachieved, and (b) the limitations inherent in the art of compoundingsuch an active compound for the treatment of sensitivity in individuals.

Therapeutic compositions typically must be sterile and stable under theconditions of manufacture and storage. The composition can be formulatedas a solution, microemulsion, liposome, or other ordered structuresuitable to high drug concentration. The carrier can be a solvent ordispersion medium containing, for example, water, ethanol, polyol (forexample, glycerol, propylene glycol, and liquid polyethylene glycol, andthe like), and suitable mixtures thereof. The proper fluidity can bemaintained, for example, by the use of a coating such as lecithin, bythe maintenance of the required particle size in the case of dispersionand by the use of surfactants. In many cases, it will be preferable toinclude isotonic agents, for example, sugars, polyalcohols such asmannitol, sorbitol, or sodium chloride in the composition. Prolongedabsorption of the injectable compositions can be brought about byincluding in the composition an agent which delays absorption, forexample, monostearate salts and gelatin.

The compounds can be administered in a time release formulation, forexample in a composition which includes a slow release polymer. Thecompounds can be prepared with carriers that will protect the compoundagainst rapid release, such as a controlled release formulation,including implants and microencapsulated delivery systems.Biodegradable, biocompatible polymers can be used, such as ethylenevinyl acetate, polyanhydrides, polyglycolic acid, collagen,polyorthoesters, polylactic acid and polylactic, polyglycolic copolymers(PLG). Many methods for the preparation of such formulations aregenerally known to those skilled in the art.

Sterile injectable solutions can be prepared by incorporating thecompound in the required amount in an appropriate solvent with one or acombination of ingredients enumerated above, as required, followed byfiltered sterilization. Generally, dispersions are prepared byincorporating the active compound into a sterile vehicle which containsa basic dispersion medium and the required other ingredients from thoseenumerated above. In the case of sterile powders for the preparation ofsterile injectable solutions, the preferred methods of preparation arevacuum drying and freeze-drying which yields a powder of the activeingredient plus any additional desired ingredient from a previouslysterile-filtered solution thereof.

In some embodiments, certain disclosed compounds are capable ofdelivering an efficacious amount of compound when administered to apatient orally. For example, in certain embodiments, certain disclosedcompounds are more efficacious when administered orally to a patient ascompared to oral administration to a patient of a peptidyl compoundrepresented by:

In accordance with an alternative aspect of the invention, a compoundmay be formulated with one or more additional compounds that enhance thesolubility of the compound.

Methods

Methods for treating cognitive disorders and for enhancing learning areprovided. Such methods include administering a pharmaceuticallyacceptable formulation of one or more of the disclosed compounds to apatient in need thereof. Also contemplated are methods of treatingpatients suffering from, memory deficits associated with aging,schizophrenia, special learning disorders, seizures, post-strokeconvulsions, brain ischemia, ischemic stroke, transient ischemic attack,cardiac ischemia, myocardial infarction, hypoglycemia, cardiac arrest,epilepsy, migraine, as well as Huntington's, Parkinson's, andAlzheimer's disease.

Other methods contemplated include the treatment of cerebral ischemia,stroke, brain trauma, brain tumors, acute neuropathic pain, chronicneuropathic pain, sleep disorders, drug addiction, depression, certainvision disorders, ethanol withdrawal, anxiety, memory and learningdisabilities, autism, epilepsy, AIDS dementia, multiple system atrophy,progressive supra-nuclear palsy, Friedrich's ataxia, Down's syndrome,fragile X syndrome, tuberous sclerosis, olivio-ponto-cerebellar atrophy,cerebral palsy, drug-induced optic neuritis, peripheral neuropathy,myelopathy, ischemic retinopathy, diabetic retinopathy, glaucoma,cardiac arrest, behavior disorders, impulse control disorders,Alzheimer's disease, memory loss that accompanies early stageAlzheimer's disease, modulating an Alzheimer's amyloid protein (e.g.,beta amyloid peptide, e.g. the isoform Aβ₁₋₄₂), in-vitro or in-vivoattention deficit disorder, ADHD (attention deficit hyperactivitydisorder), schizophrenia, amelioration of opiate, nicotine addiction,ethanol addition, traumatic brain injury, spinal cord injury,post-traumatic stress syndrome, Huntington's disease, and Huntington'schorea.

For example, provided here are methods of treating benign Rolanicepilepsy, frontal lobe epilepsy, infantile spasms, juveline myoclonicepilepsy, Lennox-Gastaut syndrome, Landau-Kleffner syndrome, Dravetsyndrome, progressive myoclonus epilepsies, reflex epilepsy, Rasmussen'ssyndrome, temporal lobe epilepsy, limbic epilepsy, status epilepticus,abdominal epilepsy, massive bilateral myoclonus, catamenial epilepsy,Jacksonian seizure disorder, Lafora disease, and/or photosensitiveepilepsy comprising administering an effective amount of a disclosedcompound.

For example, provided herein is a method of treating depression in apatient in need thereof, comprising administering a disclosed compound,e.g., by acutely administering a disclosed compound. In certainembodiments, the treatment-resistant patient is identified as one whohas been treated with at least two types of antidepressant treatmentsprior to administration of a disclosed compound. In other embodiments,the treatment-resistant patient is one who is identified as unwilling orunable to tolerate a side effect of at least one type of antidepressanttreatment.

The most common depression conditions include Major Depressive Disorderand Dysthymic Disorder. Other depression conditions develop under uniquecircumstances. Such depression conditions include but are not limited toPsychotic depression, Postpartum depression, Seasonal affective disorder(SAD), mood disorder, depressions caused by chronic medical conditionssuch as cancer or chronic pain, chemotherapy, chronic stress, posttraumatic stress disorders, and Bipolar disorder (including bipolar Idisorder, bipolar II disorder, cyclothymia, or manic depressivedisorder).

Refractory depression occurs in patients suffering from depression whoare resistant to standard pharmacological treatments, includingtricyclic antidepressants, MAOIs, SSRIs, and double and triple uptakeinhibitors and/or anxiolytic drugs, as well non-pharmacologicaltreatments such as psychotherapy, electroconvulsive therapy, vagus nervestimulation and/or transcranial magnetic stimulation. Atreatment-resistant patient may be identified as one who fails toexperience alleviation of one or more symptoms of depression (e.g.,persistent anxious or sad feelings, feelings of helplessness,hopelessness, pessimism) despite undergoing one or more standardpharmacological or non-pharmacological treatment. In certainembodiments, a treatment-resistant patient is one who fails toexperience alleviation of one or more symptoms of depression despiteundergoing treatment with two different antidepressant drugs. In otherembodiments, a treatment-resistant patient is one who fails toexperience alleviation of one or more symptoms of depression despiteundergoing treatment with four different antidepressant drugs. Atreatment-resistant patient may also be identified as one who isunwilling or unable to tolerate the side effects of one or more standardpharmacological or non-pharmacological treatment.

In some embodiments, patients suffering from autism also suffer fromanother medical condition, such as Fragile X syndrome, tuberoussclerosis, congenital rubella syndrome, and untreated phenylketonuria.

In yet another aspect, a method for enhancing pain relief and forproviding analgesia to an animal is provided.

In certain embodiments, methods for treating schizophrenia are provided.For example, paranoid type schizophrenia, disorganized typeschizophrenia (i.e., hebephrenic schizophrenia), catatonic typeschizophrenia, undifferentiated type schizophrenia, residual typeschizophrenia, post-schizophrenic depression, and simple schizophreniamay be treated using the methods and compositions contemplated herein.Psychotic disorders such as schizoaffective disorders, delusionaldisorders, brief psychotic disorders, shared psychotic disorders, andpsychotic disorders with delusions or hallucinations may also be treatedusing the compositions contemplated herein. Paranoid schizophrenia maybe characterized where delusions or auditory hallucinations are present,but thought disorder, disorganized behavior, or affective flattening arenot. Delusions may be persecutory and/or grandiose, but in addition tothese, other themes such as jealousy, religiosity, or somatization mayalso be present. Disorganized type schizophrenia may be characterizedwhere thought disorder and flat affect are present together. Catatonictype schizophrenia may be characterized where the subject may be almostimmobile or exhibit agitated, purposeless movement. Symptoms can includecatatonic stupor and waxy flexibility. Undifferentiated typeschizophrenia may be characterized where psychotic symptoms are presentbut the criteria for paranoid, disorganized, or catatonic types have notbeen met. Residual type schizophrenia may be characterized wherepositive symptoms are present at a low intensity only.Post-schizophrenic depression may be characterized where a depressiveepisode arises in the aftermath of a schizophrenic illness where somelow-level schizophrenic symptoms may still be present. Simpleschizophrenia may be characterized by insidious and progressivedevelopment of prominent negative symptoms with no history of psychoticepisodes.

In some embodiments, methods are provided for treating psychoticsymptoms that may be present in other mental disorders, including, butnot limited to, bipolar disorder, borderline personality disorder, drugintoxication, and drug-induced psychosis.

In another embodiment, methods for treating delusions (e.g.,“non-bizarre”) that may be present in, for example, delusional disorderare provided.

Also provided are methods for treating social withdrawal in conditionsincluding, but not limited to, social anxiety disorder, avoidantpersonality disorder, and schizotypal personality disorder.

Additionally, methods are provided for treating obsessive-compulsivedisorder (OCD).

In some embodiments, the patient is a mammal (e.g., a human). Forexample, the patient may be a human adult patient or a human pediatricpatient.

In some embodiments, contemplated methods relate to use of a disclosedcompound or compounds alone or in combination with one or more otheragents for manufacturing a medicament for treating a contemplatedindication.

For example, in a disclosed method, a contemplated compound, or acomposition comprising a contemplated compound and, e.g., apharmaceutically acceptable excipient, may be administered parenterallyto a patient including, but not limited to, subcutaneously andintravenously. The compound or compositions contemplated herein may alsobe administered via slow controlled i.v. infusion or by release from animplant device. In an embodiment, a disclosed method for treating acontemplated indication includes administering one dose, or one or moredoses, of a disclosed compound. In some embodiments, a patient may havesubstantial improvement in symptoms after 12 hours, after 1 day, after 1week, after 2 days, after 3 days, after 4 days, after 5 days, after 6days, or even after 8 days of a one (single) dose administration.

A therapeutically effective amount of a disclosed compound required foruse in therapy varies with the nature of the condition being treated,the length of treatment time desired, the age and the condition of thepatient, and is ultimately determined by the attending physician. Ingeneral, however, doses employed for adult human treatment typically arein the range of about 0.01 mg/kg to about 1000 mg/kg per day. The dosemay be, for example, about 1 mg/kg to about 100 mg/kg per day. Thedesired dose may be conveniently administered in a single dose, or asmultiple doses administered at appropriate intervals, for example astwo, three, four or more sub-doses per day.

A number of factors may lead to the contemplated compounds beingadministered over a wide range of dosages. When given in combinationwith other therapeutic agents, the dosage of the contemplated compoundsmay be given at relatively lower dosages. As a result, the dosage of acontemplated compound may be from about 1 ng/kg to about 100 mg/kg. Thedosage of a contemplated compound may be at any dosage including, butnot limited to, about 1 ug/kg, 25 ug/kg, 50 ug/kg, 75 ug/kg, 100 uug/kg, 125 ug/kg, 150 ug/kg, 175 ug/kg, 200 ug/kg, 225 ug/kg, 250 ug/kg,275 ug/kg, 300 ug/kg, 325 ug/kg, 350 ug/kg, 375 ug/kg, 400 ug/kg, 425ug/kg, 450 ug/kg, 475 ug/kg, 500 ug/kg, 525 ug/kg, 550 ug/kg, 575 ug/kg,600 ug/kg, 625 ug/kg, 650 ug/kg, 675 ug/kg, 700 ug/kg, 725 ug/kg, 750ug/kg, 775 ug/kg, 800 ug/kg, 825 ug/kg, 850 ug/kg, 875 ug/kg, 900 ug/kg,925 ug/kg, 950 ug/kg, 975 ug/kg, 1 mg/kg, 5 mg/kg, 10 mg/kg, 15 mg/kg,20 mg/kg, 25 mg/kg, 30 mg/kg, 35 mg/kg, 40 mg/kg, 45 mg/kg, 50 mg/kg, 60mg/kg, 70 mg/kg, 80 mg/kg, 90 mg/kg, or 100 mg/kg.

In some embodiments, a disclosed compound may be dosed at an amount thatproduces antidepressive-like and/or anxiolytic-like effects.

Disclosed compounds may be provided as part of a liquid or solidformulation, for example, aqueous or oily suspensions, solutions,emulsions, syrups, and/or elixirs. The compositions may also beformulated as a dry product for constitution with water or othersuitable vehicle before use. Such liquid preparations may containadditives including, but not limited to, suspending agents, emulsifyingagents, nonaqueous vehicles and preservatives. Suspending agentsinclude, but are not limited to, sorbitol syrup, methyl cellulose,glucose/sugar syrup, gelatin, hydroxyethylcellulose, carboxymethylcellulose, aluminum stearate gel, and hydrogenated edible fats.Emulsifying agents include, but are not limited to, lecithin, sorbitanmonooleate, and acacia. Nonaqueous vehicles include, but are not limitedto, edible oils, almond oil, fractionated coconut oil, oily esters,propylene glycol, and ethyl alcohol. Preservatives include, but are notlimited to, methyl or propyl hydroxybenzoate and sorbic acid.Contemplated compounds may also be formulated for parenteraladministration including, but not limited to, by injection or continuousinfusion. Formulations for injection may be in the form of suspensions,solutions, or emulsions in oily or aqueous vehicles, and may containformulation agents including, but not limited to, suspending,stabilizing, and dispersing agents. The composition may also be providedin a powder form for reconstitution with a suitable vehicle including,but not limited to, sterile, pyrogen-free water.

EXAMPLES

The following examples are provided for illustrative purposes only, andare not intended to limit the scope of the disclosure.

Example 1—Synthesis of Compounds of Structure A

The following reaction sequence (Scheme 1) is used to synthesizecompounds of structure A.

Example 2—Synthesis of Compounds of Structure B

The following reaction sequence (Scheme 2) is used to synthesizecompounds of structure B.

Example 3—Synthesis of Compounds of Structure C

In some embodiments, the following reaction sequence (Scheme 3) can beused to synthesize compounds of formula (III), e.g., structure C below.

In other embodiments, compounds of formula (III) can be preparedaccording to Scheme 4 below, in which the proline nitrogen atom of theleft hand fragment is already substituted with the amino acid unit thatis installed in the last step of Scheme 3 above.

R* in Scheme 4 represents the C(R¹)(R²)(R¹¹) portion of formula (III).R²¹⁻²³ in Scheme 4 represents any substitution pattern encompassed bythe definitions of R²¹, R²², and R²³ provided herein. The left handfragment and right hand fragment (Trp(Boc)-Thr(OtBu)-CONH₂) can becoupled using peptide coupling agents, such as HBTU, HATU, BOP or pyBOP,which have been shown to be suitable for amidation of conformationallyconstrained amino acids. Global deprotection of the side chain groups(Boc and tBu) can be achieved, e.g., by treatment of the product of step1 with, e.g., trifluoroacetic acid in dichloromethane (DCM), to furnishthe desired tetrapeptides.

In some embodiments, the right hand fragment can be prepared accordingto Scheme 5 below.

As shown in step 1 of Scheme 5, Fmoc-Trp-(Boc)-OH and Thr(O^(t)Bu)-CONH₂can be coupled under conventional conditions using, e.g., DIC/HOBt orEDC/HOBt, to afford the protected dipeptide. Fmoc-Trp-(Boc)-OH can beprepared using conventional methods or obtained commercially; andThr(OtBu)-CONH₂ can be prepared, e.g., in two steps from Z-Thr(OtBu)-OH.Fmoc deprotection under basic conditions (e.g., diethylamine/DCM atambient temperature) can provide the desired dipeptide suitable forend-game coupling strategy.

In some embodiments, the left hand fragment can be prepared according toScheme 6 below.

R* in Scheme 6 represents the C(R¹)(R²)(R¹¹)portion of formula (III).R²¹⁻²³ in Scheme 6 represents any substitution pattern set encompassedby the definitions of R²¹, R²², and R²³ provided herein. In certainembodiments, the left hand fragment include one or two unnatural aminoacids. Typically, 5-10 reactions steps are involved in the synthesis ofunnatural analogues of the proline and α-substituted L-glycine aminoacid starting materials used in step 1. Substituted beta-hydroxy aminoacids can be prepared by Peterson's Aldol approach. Amidation usingpeptide coupling agents, e.g., HBTU, HATU, BOP or pyBOP, can be used forassembly of the left-hand side dipeptides constituted by unnatural aminoacids. Exemplary left hand fragments are delineated in FIG. 3.

A. Synthesis of NRX-4001 & 4006:

Synthesis of(S)-2-((tert-butoxycarbonyl)amino)-3-(1H-indol-3-yl)propanoic acid (2)

To a stirred solution of compound 1 (30 g, 147 mmol) in THF:H₂O (1:1,180 mL), sodium bicarbonate (24.7 g, 294 mmol) and di-tertiary butyldicarbonate (35.2 g, 161 mmol) were added at 10-15° C. and the reactionmixture was allowed to stir at room temperature for 12 h. Aftercompletion of the reaction as indicated by TLC, the reaction mixture wasconcentrated under reduced pressure to obtain a residue and the residuewas treated with MTBE and acidified to pH 2-3 using 1N HCl. Theprecipitated solid was stirred for 1 h in MTBE and filtered. Thefiltered solid was washed by stirring in water for 1 h, filtered, anddried to afford compound 2 (35.0 g, 79%).

MS (ESI) m/z 305 [M+1]⁺.

Synthesis of tert-butyl((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamate(4)

To a stirred solution of compound 2 (5 g, 16.4 mmol) in DCM (50 mL),HATU (9.36 g, 24.6 mmol) and diisopropylethylamine (10 mL, 49.26 mmol)were added. The solution was stirred at rt for 35 min to generate theactivated ester to which compound 3 (1.92 g, 16.4 mmol) was added andstirred at room temperature for 12 h. The progress of the reaction wasmonitored by TLC & LCMS. After complete consumption of startingmaterial, the reaction was quenched with water and extracted with 10%methanol in DCM. The organic layers were washed with sodium bicarbonatesolution and brine, dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to obtain a crude residue, which was purified by columnchromatography to afford compound 4 (5.2 g, 78%).

MS (ESI) m/z 405 [M+1]⁺.

Synthesis of(2S,3R)-2-((S)-2-amino-3-(1H-indol-3-yl)propanamido)-3-hydroxybutanamide(5)

To a stirred solution of compound 4 (5.2 g, 12.8 mmol) in DCM (25 mL),TFA (25 mL) was added at 0° C. and the reaction mixture was stirred atrt for 2 h. The progress of the reaction was monitored by TLC & LCMS.After complete consumption of compound 4, the solvent was removed underreduced pressure to obtain a crude residue. The residue was dissolved inwater and extracted with ethyl acetate. The aqueous layer wasneutralized with saturated sodium bicarbonate solution and concentratedunder reduced pressure to obtain a crude residue, which was purified byflash column chromatography to afford compound 5 (2.8 g, 71%).

MS (ESI) m/z 305 [M+1]⁺.

Synthesis of (S)-tert-butyl2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(6)

To a stirred solution of compound B (0.5 g, 2.32 mmol) in DCM (20 mL),HATU (1.32 g, 3.48 mmol) and diisopropylethylamine (1.21 mL, 6.96 mmol)were added. The solution was stirred at room temperature for 35 min togenerate the activated ester to which compound 5 (0.77 g, 2.55 mmol) wasadded and stirred at room temperature for 12 h. The progress of thereaction was monitored by TLC & LCMS. After complete consumption ofstarting material, the reaction was quenched with water and extractedwith DCM. The organic layer was washed with sodium bicarbonate solutionand brine, dried over anhydrous Na₂SO₄ and concentrated under reducedpressure to obtain a crude residue, which was purified by columnchromatography to afford compound 6 (0.71 g, 63%).

MS (ESI) m/z: 402 [M−BOC]⁺.

Synthesis of(S)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)pyrrolidine-2-carboxamide(NRX-4006)

To a stirred solution of compound 6 (0.71 g, 1.41 mmol) in dioxane (5mL), 4 M dioxane: HCl (8 mL) was added at 0° C. and the reaction mixturewas stirred at rt for 3 h. The progress of the reaction was monitored byTLC & LCMS. After complete consumption of compound 6, the solvent wasremoved under reduced pressure to obtain a crude residue, which waspurified by Prep HPLC to obtain NRX-4006 (0.1 g, 17.5%) as an off-whitesolid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.83 (s, 1H), 8.34-8.24 (m, 2H), 7.80 (d,J=8.6 Hz, 1H), 7.57 (d, J=7.9 Hz, 1H), 7.31 (d, J=8.0 Hz, 1H), 7.13 (d,J=7.4 Hz, 2H), 7.15-7.13 (m, 1H), 6.99-6.85 (m, 1H), 4.63 (td, J=8.3,4.6 Hz, 1H), 4.17-3.97 (m, 2H), 3.59 (dd, J=8.6, 5.2 Hz, 1H), 3.18 (dd,J=14.7, 4.8 Hz, 1H), 3.04 (dd, J=14.7, 8.6 Hz, 1H), 2.82-2.75 (m, 1H),2.59-2.57 (m, 1H), 1.85-1.91 (m, 1H), 1.61-1.29 (m, 3H), 1.00 (d, J=6.3Hz, 3H).

HPLC purity: 96.6%

LCMS Calculated for C₂₀H₂₂N₅O₄: 401.47; Observed: 402.25 [M+1]⁺.

Synthesis of benzyl((2S,3R)-1-((S)-2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(7)

To a stirred solution of compound D (0.63 g, 2.48 mmol) in DCM (40 mL),HATU (1.41 g, 3.72 mmol) and diisopropylethylamine (1.28 mL, 7.44 mmol)were added. The solution was stirred at room temperature for 30 min towhich NRX-4006 (1 g, 2.48 mmol) was added and stirred at roomtemperature for 12 h. The progress of the reaction was monitored by TLC& LCMS. After complete consumption of starting material, the reactionwas quenched with water and extracted with DCM. The organic layers werewashed with brine, dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to obtain a crude residue, which was purified by columnchromatography to afford compound 7 (0.65 g, 42%).

MS (ESI) m/z: 637 [M+1]⁺.

Synthesis of(S)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-1-((2S,3R)-2-amino-3-hydroxybutanoyl)pyrrolidine-2-carboxamide(NRX-4001)

To a stirred solution of compound 7 (0.650 g, 1.05 mmol) in methanol (20mL), 10% palladium-carbon (0.08 g) was added and the reaction mixturewas stirred under hydrogen atmosphere at bladder pressure at roomtemperature for 12 h. The progress of the reaction was monitored by TLC.After complete consumption of starting material, the reaction mixturewas filtered through a pad of celite and filtrate was concentrated underreduced pressure to obtain a crude residue, which was purified by PrepHPLC (Basic method) to afford compound NRX-4001 (0.480 g, 91%) as anoff-white solid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.88-10.80 (m, 1H), 8.33 (s, 3H),8.08-7.99 (m, 1H), 7.57 (dd, J=15.8, 7.9 Hz, 2H), 7.31 (d, J=8.1 Hz,1H), 7.17-6.92 (m, 4H), 4.65-4.60 (m. 1H), 4.58-4.44 (m, 2H), 4.34 (d,J=8.0 Hz, 1H), 4.05-3.99 (m, 2H), 3.58 (d, J=18.7 Hz, 3H), 3.24-3.12 (m,1H), 3.11-2.95 (m, 1H), 2.48-2.43 (m, 1H), 1.97 (s, 1H), 1.77-1.64 (m,3H), 1.08-0.98 (m, 6H).

HPLC purity: 94.1%

LCMS Calculated for C₂₄H₃₄N₆O₆: 502.57; Observed: 503.55 [M+1]⁺.

B. Synthesis of NRX-4002:

Synthesis of1-(tert-butyl)-2-methyl-(2S,4R)-4-(benzyloxy)pyrrolidine-1,2-dicarboxylate(2)

To a stirred solution of compound 1 (2.65 g, 10.80 mmol) in DMF (75 mL),sodium hydride (0.570 g, 23.75 mmol) was added at 0° C. and stirred for10 min. The reaction mixture was treated with benzyl bromide (1.39 mL,11.69 mmol) in DMF (10 mL) and stirred at room temperature for 16 h. Thereaction mixture was concentrated under reduced pressure and the residuewas treated with water and extracted with ethyl acetate. The organiclayers were washed with brine, separated, dried over sodium sulphate andconcentrated under reduced pressure to afford compound 2 (3.45 g, 96%).

MS (ESI) m/z 336 [M+1]⁺.

Synthesis of(2S,4R)-4-(benzyloxy)-1-(tert-butoxycarbonyl)pyrrolidine-2-carboxylicacid (3)

To a solution of compound 2 (3.45 g, 10.29 mmol) in THF:H₂O (60 mL, 2:1)lithium hydroxide monohydrate (1.29 g, 30.87 mmol) was added and thereaction mixture was stirred at room temperature for 3 h. Aftercompletion of the reaction as indicated by TLC the reaction mixture wasconcentrated under reduced pressure, acidified with 1N hydrochloric acidand extracted with ethyl acetate. The organic layers were separated,washed with brine, dried over Na₂SO₄ and concentrated under reducedpressure to obtain the crude residue. The residue was purified bytrituration with pentene to afford compound 3 (3.21 g, 97%).

MS (ESI) m/z 322 [M+1]⁺.

Synthesis oftert-butyl-(2S,4R)-2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-4-(benzyloxy)pyrrolidine-1-carboxylate(5)

To a stirred solution of compound 3 (1 g, 3.11 mmol) in DCM (20 mL),HATU (1.7 g, 4.6 mmol) and diisopropylethylamine (1.6 mL, 9.33 mmol)were added. The solution was stirred at rt for 1 h to generate theactivated ester and treated with compound 4 (0.947 g, 3.11 mmol) andstirred at room temperature for 12 h. The progress of the reaction wasmonitored by TLC & LCMS. After complete consumption of startingmaterial, the reaction was quenched with water and extracted with DCM.The organic layers were washed with sodium bicarbonate solution andbrine, dried over anhydrous Na₂SO₄ and concentrated under reducedpressure to obtain a crude residue, which was purified by columnchromatography to afford compound 5 (1.23 g, 65%).

LCMS: 508 (M−Boc)⁺.

Synthesis of(2S,4R)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-4-(benzyloxy)pyrrolidine-2-carboxamide(6)

To a stirred solution of compound 5 (1.23 g, 2.02 mmol) in dioxane (5mL), 4 M HCl in dioxane (12 mL) was added at 0° C. and the reactionmixture was stirred at room temperature for 3 h. The progress of thereaction was monitored by TLC & LCMS. After complete consumption ofcompound 5, the solvent was removed under reduced pressure to obtain acrude residue, which was purified by trituration with DCM to affordcompound 6 (1 g, 90%).

MS (ESI) m/z 508 [M+1]⁺.

Synthesis of benzyl((2S,3R)-1-((2S,4R)-2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-4-(benzyloxy)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(8)

To a stirred solution of compound 7 in DCM (30 mL), HATU (1.1 g, 2.94mmol) and diisopropylethylamine (1 mL, 5.88 mmol) were added. Thesolution was stirred at room temperature for 1 h to generate theactivated ester to which compound 6 (1 g, 1.96 mmol) was added andstirred at room temperature for 12 h. The progress of the reaction wasmonitored by TLC & LCMS. After complete consumption of startingmaterial, the reaction was quenched with water and extracted with DCM.The organic layers were washed with sodium bicarbonate solution andbrine, dried over anhydrous Na₂SO₄ and concentrated under reducedpressure to obtain a crude residue, which was purified by columnchromatography to afford compound 8 (0.950 g, 65%).

MS (ESI) m/z: 743 (M+1)⁺.

Synthesis of(2S,4R)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-1-((2S,3R)-2-amino-3-hydroxybutanoyl)-4-hydroxypyrrolidine-2-carboxamide(NRX-4002)

To a stirred solution of compound 8 (0.55 g, 0.74 mmol) in methanol (40mL), 20% palladium hydroxide (0.06 g) and acetic acid (0.1 mL) wereadded and the reaction mixture was stirred under hydrogen atmosphere atbladder pressure at room temperature for 12 h. The progress of thereaction was monitored by TLC. After complete consumption of startingmaterial, the reaction mixture was filtered through a pad of celite andthe filtrate was concentrated under reduced pressure to obtain a cruderesidue, which was purified by Prep HPLC (Basic method) to affordcompound NRX-4002. Data for two different batches is a follows:

Batch-I:

Yield: 0.02 g as an off-white solid; ¹H NMR (400 MHz, DMSO-d₆) δ:10.88-10.78 (m, 1H), 8.35 (s, 2H), 8.16 (t, J=6.8 Hz, 1H), 7.63-7.43 (m,2H), 7.32 (d, J=8.0 Hz, 1H), 7.26-7.13 (m, 1H), 7.17.03 (m, 5H),4.65-4.60 (m, 1H), 4.5-4.44 (m, 2H), 4.24-4.11 (m, 1H), 4.16-3.98 (m,2H), 3.75-3.33 (m, 3H), 3.27-3.06 (m, 1H), 3.09-2.90 (m, 1H), 2.02-1.91(m, 1H), 1.73-1.53 (m, 1H), 1.16-0.88 (m, 6H); HPLC purity: 91.48%; LCMSCalculated for C₂₄H₃₄N₆O₂: 518.57; Observed: 519.45 [M+1]⁺.

Batch-II:

Yield: 0.04 g as an off-white solid; ¹H NMR (400 MHz, DMSO-d₆) δ: ¹H NMR(400 MHz, DMSO-d₆) δ: 10.87-10.76 (m, 1H), 8.32 (s, 2H), 8.10 (d, J=7.5Hz, 1H), 7.63-7.43 (m, 2H), 7.32 (d, J=8.0 Hz, 1H), 7.24-6.92 (m, 6H),4.65-4.60 (m, 1H), 4.56-4.33 (m, 3H), 4.24-4.11 (m, 1H), 4.11-4.04 (m,3H), 3.70-3.54 (m, 1H), 3.52-3.29 (m, 2H), 3.27-3.19 (m, 1H), 3.18 (dd,J=14.9, 4.8 Hz, 1H), 3.10-3.05 (m, 1H), 1.96 (dd, J=13.2, 8.0 Hz, 1H),1.71-1.56 (m, 1H), 1.13-0.91 (m, 6H); HPLC purity: 93.7%; LCMSCalculated for C₂₄H₃₄N₆O₇: 518.57; Observed: 519.45 [M+1]⁺.

C. Synthesis of NRX-4007:

Synthesis of(2S,4R)-1-(tert-butoxycarbonyl)-4-hydroxypyrrolidine-2-carboxylic acid(2)

To a stirred solution of compound 1 (1.2 g, 7.35 mmol) indichloromethane (50 mL), N,N-dimethylaminopyridine (0.898 g, 7.35 mmol)followed by di-tertiary butyl dicarbonate (3.2 g, 14.70 mmol) were addedand the reaction mixture was allowed to stir at room temperature for 6h. The reaction mixture was quenched with water and the compound wasextracted in ethyl acetate. The organic layers were washed with 0.5 MHCl and brine, separated, dried over sodium sulphate and concentratedunder reduced pressure. The residue was purified by silica gel columnchromatography using 1-2% methanol in dichloromethane as eluent toafford compound 2 (1.75 g, 92%).

MS (ESI) m/z 232 [M+1]⁺.

Synthesis of (2S,4R)-tert-butyl2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-4-hydroxypyrrolidine-1-carboxylate(4)

To a stirred solution of compound 2 (1.5 g, 6.49 mmol) in DCM (30 mL),HATU (3.7 g, 9.73 mmol) and diisopropylethylamine (3.4 mL, 19.47 mmol)were added. The solution was stirred at room temperature for 1 h to formthe activated ester and treated with compound 3 (2.1 g, 7.14 mmol) andstirred for 12 h. The progress of the reaction was monitored by TLC &LCMS. After complete consumption of starting material, the reaction wasquenched with 1N HCl solution and extracted with DCM. The organic layerwas washed with sodium bicarbonate solution and brine, dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to obtain acrude residue, which was purified by column chromatography to affordcompound 4 (2.15 g, 59%).

MS (ESI) m/z 418.2 [M−Boc]⁺.

Synthesis of(2S,4R)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-4-hydroxypyrrolidine-2-carboxamide(NRX-4007)

To a stirred solution of compound 4 (2.15 g, 4.15 mmol) in dioxane (10mL), 4 M HCl in dioxane (20 mL) was added at 0° C. and the reactionmixture was stirred at rt for 2 h. The progress of the reaction wasmonitored by TLC & LCMS. After complete consumption of compound 4, thesolvent was removed under reduced pressure to obtain a crude residue,which was purified by Prep HPLC (Basic method) to obtain compoundNRX-4007 (0.125 g, 7.2%) as an off-white solid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.80 (d, J=2.5 Hz, 1H), 8.12 (d, J=8.1 Hz,1H), 7.82 (d, J=8.6 Hz, 1H), 7.52 (d, J=7.9 Hz, 1H), 7.30 (d, J=8.0 Hz,1H), 7.21-6.89 (m, 5H), 4.62-4.58 (m, 1H), 4.13 (dd, J=8.6, 3.6 Hz, 1H),4.06-3.89 (m, 2H), 3.62 (t, J=8.1 Hz, 1H), 3.16 (dd, J=14.6, 4.8 Hz,1H), 3.04 (dd, J=14.7, 8.2 Hz, 1H), 2.62-2.50 (m, 1H), 2.31 (dd, J=11.6,3.8 Hz, 1H), 1.82-1.78 (m, 1H), 1.40-1.37 (m, 1H), 1.00 (d, J=6.3 Hz,3H).

HPLC purity: 91.2%

LCMS Calculated for C₂₀H₂₂N₅O₅: 417.47; Observed: 418.40 [M+1]⁺.

D. Synthesis of NRX-4003 and O-Acetyl Tripeptide:

Synthesis of(2S,4R)-4-acetoxy-1-(tert-butoxycarbonyl)-pyrrolidine-2-carboxylic acid(2)

To a solution of compound 1 (3 g, 12.9 mmol) in pyridine (30 mL), aceticanhydride (13.18 g, 129.3 mmol) was added. The reaction mixture wasstirred at room temperature for 16 h. After completion of the reactionas indicated by TLC, the reaction mixture was concentrated under reducedpressure to obtain a crude residue. The residue was azeotroped withtoluene and dried to afford compound 2. The compound was use as such forthe next step (2.5 g, crude).

MS (ESI) m/z 274 [M+1]⁺.

Synthesis of tert-butyl-(2S,4R)4-acetoxy-2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(4)

To a stirred solution of compound 2 (1.5 g, 5.47 mmol) in DCM (20 mL),HATU (3.09 g, 8.21 mmol) and diisopropylethylamine (2.85 mL, 16.4 mmol)were added. The solution was stirred at room temperature for 1 h togenerate the activated ester and treated with compound 3 (1.83 g, 6.02mmol) and stirred at room temperature for 12 h. The progress of thereaction was monitored by TLC & LCMS. After complete consumption ofstarting material, the reaction was quenched with 1N HCl solution andextracted with DCM. The organic layers were washed with saturated sodiumbicarbonate solution and brine, dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to obtain a crude residue, which waspurified by column chromatography to afford compound 4 (2.25 g, 73%).

MS (ESI) m/z 450 [M−Boc]⁺.

Synthesis of(3R,5S)-5-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)pyrrolidin-3-ylacetate (O-acetyl tripeptide) (NRX-4013)

To a stirred solution of compound 4 (2.2 g, 3.93 mmol) in dioxane (5mL), 4 M HCl in dioxane (20 mL) was added at 0° C. and the reactionmixture was stirred at rt for 2 h. The progress of the reaction wasmonitored by TLC & LCMS. After complete consumption of compound 2, thesolvent was removed under reduced pressure to obtain a crude residue,which was purified by Prep HPLC (Basic method) to afford O-acetyltripeptide NRX-4013 (1.65 g, 91.6%) as an off-white solid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.81 (d, J=2.3 Hz, 1H), 8.21 (s, 1H), 8.11(d, J=8.1 Hz, 1H), 7.83 (d, J=8.6 Hz, 1H), 7.53 (d, J=7.9 Hz, 1H), 7.30(d, J=8.0 Hz, 1H), 7.18-6.90 (m, 5H), 4.84 (t, J=4.7 Hz, 1H), 4.64 (td,J=8.1, 4.9 Hz, 1H), 4.14 (dd, J=8.6, 3.7 Hz, 1H), 4.07-3.96 (m, 1H),3.70-3.62 (m, 1H), 3.18 (dd, J=14.5, 4.8 Hz, 1H), 3.04 (dd, J=14.6, 8.1Hz, 1H), 2.75 (d, J=12.8 Hz, 1H), 2.62-2.53 (m, 1H), 2.42-2.39 (m, 2H),1.95 (s, 3H), 1.65-1.58 (m, 1H), 1.04 (dd, J=27.1, 6.5 Hz, 4H).

HPLC purity: 96.14%

LCMS Calculated for C₂₂H₂₉N₅O₆: 459.50; Observed: 461[M+1]⁺.

Synthesis of(3R,5S)-5-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-1-((2S,3R)-2-((tert-butoxycarbonyl)amino)-3-hydroxybutanoyl)pyrrolidin-3-ylacetate (6)

To a stirred solution of compound 5 (0.76 g, 3.47 mmol) in DCM (50 mL),HATU (1.98 g, 5.21 mmol) and diisopropylethylamine (1.79 g, 16.4 mmol)were added. The solution was stirred at rt for 1 h to generate theactivated ester to which O-acetyl tripeptide NRX-4013 (1.6 g, 13.9 mmol)in DCM was added and stirred at rt for 12 h. The progress of thereaction was monitored by TLC & LCMS. After complete consumption ofstarting material, the reaction was quenched with 1N HCl solution andextracted with DCM. The organic layers were washed with sodiumbicarbonate solution and brine, dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to obtain a crude residue, which waspurified by column chromatography to afford compound 6 (1.5 g, 65%).

MS (ESI) m/z 561 [M−Boc]⁺.

Synthesis of(3R,5S)-5-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-1-((2S,3R)-2-amino-3-hydroxybutanoyl)pyrrolidin-3-yl acetate (NRX-4003)

To a stirred solution of compound 6 (1.0 g, 1.51 mmol) in dioxane (4mL), 4 M HCl in dioxane (10 mL) was added at 0° C. and the reactionmixture was stirred at room temperature for 2 h. The progress of thereaction was monitored by TLC & LCMS. After complete consumption ofcompound 6, the solvent was removed under reduced pressure to obtain acrude residue, which was purified by Prep HPLC (Basic method) to obtainNRX-400 (0.8 g, 94.3%) as an off-white solid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.82 (d, J=19.1 Hz, 1H), 8.30 (s, 2H),8.23 (d, J=7.5 Hz, 1H), 7.64-7.49 (m, 2H), 7.32 (d, J=8.1 Hz, 1H), 7.23(s, 1H), 7.16 (s, 2H), 7.13-6.92 (m, 4H), 5.15 (s, 1H), 4.78-4.60 (m,2H), 4.10-3.98 (m, 2H), 3.87-3.71 (m, 2H), 3.63 (t, J=6.3 Hz, 1H), 3.39(d, J=6.4 Hz, 1H), 3.21-2.98 (m, 4H), 3.01 (dd, J=15.8, 9.3 Hz, 1H),2.18 (dd, J=14.6, 8.1 Hz, 1H), 2.00 (s, 2H), 1.92 (d, J=22.3 Hz, 1H),1.09 (d, J=6.2 Hz, 2H), 0.99 (dd, J=24.2, 6.4 Hz, 5H).

Hplc Purity: 97.2%

LCMS Calculated for C₂₆H₃₆N₆O₈: 560.61; Observed: 561.55[M+1]⁺.

E. Synthesis of NRX-4004 & 4008:

Synthesis of (2S,4R)-methyl 4-hydroxypyrrolidine-2-carboxylate (2)

To a stirred solution of compound 1 (20 g, 152.6 mmol) in methanol (200mL) acetyl chloride (23.93 g, 305.3 mmol) was added over a period of 30min at 0° C. and the reaction mixture was stirred at room temperaturefor 16 h. The reaction mixture was concentrated under reduced pressure.The residue was washed with ether and purified by silica gel columnchromatography using 10% methanol in dichloromethane as eluent to affordcompound 2 (25.1 g, crude).

MS (ESI) m/z 146 [M+1]⁺.

Synthesis of (2S,4R)-1-tert-butyl 2-methyl4-hydroxypyrrolidine-1,2-dicarboxylate (3)

To a stirred solution of compound 2 (26 g, 180.5 mmol) indichloromethane (400 mL), N,N-dimethylaminopyridine (1.10 g, 9.02 mmol),triethylamine (50 mL, 361.1 mmol) followed by di-tertiary butyldicarbonate (58 mL, 252.7 mmol) were added and the reaction mixture wasallowed to stir at room temperature for 12 h. After completion of thereaction as indicated by TLC, the residue was taken in ether. Theprecipitated solid was filtered and washed with ether. The ether layerwas concentrated under reduced pressure to obtain a residue The residuewas dissolved in DCM and washed with sodium bicarbonate solution. Theorganic layer was separated and dried over sodium sulphate andconcentrated under reduced pressure. The residue was purified by silicagel column chromatography using 1-2% methanol in dichloromethane aseluent to afford compound 3 as white solid (30.1 g, 67.8%).

MS (ESI) m/z 246[M+1]⁺.

Synthesis of (2S,4R)-1-tert-butyl 2-methyl4-methoxypyrrolidine-1,2-dicarboxylate (4)

To a stirred solution of compound 3 (5 g, 20.49 mmol) in THF (50 mL),sodium hydride (0.9 g, 22.53 mmol, 60%) was added portion wise over aperiod of 30 min. The reaction mixture was treated with methyl iodide(6.38 mL, 102.4 mmol) and 18-crown-6 (3.24 g, 12.29 mmol) and stirred atroom temperature for 6 h. The reaction completion was monitored by TLC.After complete consumption of starting material, the reaction wasquenched with 1N HCl solution and extracted with ethyl acetate. Theorganic layers were separated, washed with saturated sodium bicarbonatesolution and brine, dried over Na₂SO₄ and concentrated under reducedpressure to obtain a crude residue, which was purified by columnchromatography to afford compound 4 (5 g, 90%).

MS (ESI) m/z 260[M+1]⁺.

Synthesis of(2S,4R)-1-(tert-butoxycarbonyl)-4-methoxypyrrolidine-2-carboxylic acid(5)

To a solution of compound 4 (5 g, 19.3 mmol) in THF: water (35 mL, 6:1)lithium hydroxide monohydrate (1.22 g, 29.06 mmol) was added and thereaction mixture was stirred at room temperature for 2 h. The reactioncompletion was monitored by TLC. The reaction mixture was concentratedunder reduced pressure, acidified with 1N hydrochloric acid andextracted with 5% methanol in DCM. The organic layer was separated,washed with brine, dried over Na₂SO₄ and concentrated under reducedpressure to obtain crude residue of compound 5. The compound was used assuch for the next step without further purification (4.5 g, crude).

MS (ESI) m/z 246[M+1]⁺.

Synthesis of (2S,4R)-tert-butyl2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-4-methoxypyrrolidine-1-carboxylate(7)

To a stirred solution of compound 5 (0.5 g, 2.04 mmol) in DCM (20 mL),HATU (1.16 g, 3.06 mmol) and diisopropylethylamine (1.05 g, 6.12 mmol)were added. The solution was stirred at rt for 1 h and treated withcompound 6 (0.682 g, 2.24 mmol) and stirred at same temperature for 12h. The progress of the reaction was monitored by TLC & LCMS. Aftercomplete consumption of starting material, the reaction was quenchedwith 1N HCl solution and extracted with DCM. The organic layer waswashed with sodium bicarbonate solution and brine, dried over anhydrousNa₂SO₄ and concentrated under reduced pressure to obtain a cruderesidue, which was purified by column chromatography to afford compound7 (0.6 g, 53%).

MS (ESI) m/z 432 (M−Boc)⁺.

Synthesis of(2S,4R)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-4-methoxypyrrolidine-2-carboxamide(NRX-4008)

To a stirred solution of compound 7 (0.45 g, 0.847 mmol) in dioxane (3mL), 4 M HCl in dioxane (5 mL) was added at 0° C. and the reactionmixture was stirred at rt for 2 h. The progress of the reaction wasmonitored by TLC & LCMS. After complete consumption of compound 7, thesolvent was removed under reduced pressure to obtain a crude residue,which was purified by Prep HPLC (Basic method) to obtain compoundNRX-4008 (0.12 g, 32.8%) as an off-white solid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.83 (s, 1H), 8.13 (d, J=8.9 Hz, 1H), 7.86(d, J=8.6 Hz, 1H), 7.53 (d, J=7.9 Hz, 1H), 7.30 (d, J=7.9 Hz, 1H),7.23-6.99 (m, 4H), 6.94 (t, J=7.3 Hz, 1H), 5.34 (s, 1H), 5.04 (s, 2H),4.63 (q, J=6.9 Hz, 1H), 4.13 (dd, J=8.5, 3.6 Hz, 1H), 4.05-4.10 (m, 1H),3.62-3.55 (m, 2H), 3.23-2.99 (m, 5H), 2.76 (d, J=13.1 Hz, 1H), 1.93 (dd,J=13.5, 8.3 Hz, 1H), 1.43-1.39 (m, 1H), 1.00 (d, J=6.2 Hz, 3H).

HPLC purity: 95%

LCMS Calculated for C₂₁H₂₉N₅O₅: 431.49; Observed: 432.13[M+1]⁺.

Synthesis of tert-butyl((2S,3R)-1-02S,4R)-2-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-4-methoxypyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(8)

To a stirred solution of compound(2S,3R)-2-((tert-butoxycarbonyl)amino)-3-hydroxybutanoic acid (0.5 g,2.32 mmol) in DMF (10 mL), HATU (1.32 g, 3.48 mmol) anddiisopropylethylamine (1.61 mL, 9.28 mmol) were added. The solution wasstirred at rt for 1 h to which NRX-4008 (1 g, 2.32 mmol) was added andstirred at rt for 12 h. The progress of the reaction was monitored byTLC & LCMS. After complete consumption of starting material, thereaction was quenched with 1N HCl solution and extracted with DCM. Theorganic layer was washed with sodium bicarbonate solution and brine,dried over anhydrous Na₂SO₄ and concentrated under reduced pressure toobtain a crude residue, which was purified by column chromatography toafford compound 8 (1.10 g, 75%).

LCMS: 533 (M−Boc)⁺.

Synthesis of(2S,4R)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-1-((2S,3R)-2-amino-3-hydroxybutanoyl)-4-methoxypyrrolidine-2-carboxamide(NRX-4004)

To a stirred solution of compound 8 (1 g, 1.58 mmol) in dioxane (5 mL),4 M HCl in dioxane (10 mL) was added at 0° C. and the reaction mixturewas stirred at room temperature for 2 h. The progress of the reactionwas monitored by TLC & LCMS. After complete consumption of compound 8,the solvent was removed under reduced pressure to obtain a cruderesidue, which was purified by Prep HPLC (Basic method) to obtaincompound NRX-4004 (0.12 g, 14.2%) as an off-white solid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.84 (d, J=14.2 Hz, 1H), 8.34 (s, 2H),8.19 (d, J=7.4 Hz, 1H), 7.68-7.47 (m, 2H), 7.32 (d, J=8.0 Hz, 1H), 7.22(d, J=2.4 Hz, 1H), 7.19-6.92 (m, 4H), 4.58-4.39 (m, 1H), 4.34 (t, J=8.0Hz, 1H), 4.10-4.04 (m, 2H), 3.85 (s, 1H), 3.77 (d, J=11.4 Hz, 1H),3.72-3.43 (m, 3H), 3.28-2.93 (m, 5H), 2.11 (p, J=9.0, 8.1 Hz, 1H),1.76-1.72 (m, 1H), 1.18-0.88 (m, 6H).

HPLC purity: 96.5%

LCMS Calculated for C₂₅H₃₆N₆O₇: 532.60; Observed: 533.5[M+1]⁺.

F. Synthesis of NRX-4010:

Synthesis of(1S,3S,5S)-2-(tert-butoxycarbonyl)-2-azabicyclo[3.1.0]hexane-3-carboxylicacid (2)

To a stirred solution of compound 1 (0.9 g, 3.73 mmol) in aqueoussolution of sodium bicarbonate (0.894 g, 4.10 mmol),di-tert-butyl-dicarbonate (0.941 g, 11.2 mmol) in THF (25 mL) was addeddrop wise at 0° C. The reaction mixture was allowed to stir at roomtemperature for 15 h. The reaction mixture was neutralized with 3Nhydrochloric acid to pH 2 and extracted with ethyl acetate. The organiclayers was separated, dried over sodium sulphate and concentrated underreduced pressure to afford compound 2 (1.20 g, 94%).

MS (ESI) m/z 228 [M+1]⁺.

Synthesis of (1S,3S,5S)-tert-butyl3-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-2-azabicyclo[3.1.0]hexane-2-carboxylate(4)

To a stirred solution of compound 2 (1.5 g, 4.39 mmol) in DCM (20 mL),HATU (2.50 g, 6.58 mmol) and diisopropylethylamine (2.29 mL, 13.1 mmol)were added. The solution was stirred at room temperature for 1 h towhich compound 3 (1.46 g, 4.83 mmol) was stirring was continued for 12h. The progress of the reaction was monitored by TLC & LCMS. Aftercomplete consumption of starting material, the reaction was quenchedwith 1N HCl solution and extracted with DCM. The organic layers werewashed with sodium bicarbonate solution and brine, dried over anhydrousNa₂SO₄ and concentrated under reduced pressure to obtain a cruderesidue, which was purified by column chromatography to afford compound4 (1.25 g, 55.5%).

MS (ESI) m/z 414 [M−Boc]⁺.

Synthesis of(1S,3S,5S)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-2-azabicyclo[3.1.0]hexane-3-carboxamide(5)

To a stirred solution of compound 4 (1 g, 1.94 mmol) in dioxane (5 mL),4 M HCl in dioxane (10 mL) was added at 0° C. and the reaction mixturewas stirred at room temperature for 2 h. The progress of the reactionwas monitored by TLC & LCMS. After complete consumption of compound 4,the solvent was removed under reduced pressure to obtain a cruderesidue, which was purified by trituration with hexane to obtaincompound 5 (0.8 g, 99.3%).

MS (ESI) m/z 414[M+1]⁺.

Synthesis of tert-butyl((2S,3R)-1-41S,3S,5S)-3-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)-2-azabicyclo[3.1.0]hexan-2-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(6)

To a stirred solution of(2S,3R)-2-((tert-butoxycarbonyl)amino)-3-hydroxybutanoic acid (0.466 g,2.13 mmol) in DCM (20 mL), HATU (1.10 g, 2.90 mmol) anddiisopropylethylamine (1.01 mL, 5.81 mmol) were added. The solution wasstirred at room temperature for 1 h to which compound 5 (0.8 g, 1.93mmol) was added and stirring was continued for 12 h. The progress of thereaction was monitored by TLC & LCMS. After complete consumption ofstarting material, the reaction was quenched with 1N HCl solution andextracted with DCM. The organic layers were washed with sodiumbicarbonate solution and brine, dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to obtain a crude residue, which waspurified by column chromatography to afford compound 6 (1.05 g, 88.9%).

MS (ESI) m/z 515 [M−Boc]⁺.

Synthesis of(1S,3S,5S)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-2-((2S,3R)-2-amino-3-hydroxybutanoyl)-2-azabicyclo[3.1.0]hexane-3-carboxamide(NRX-4010)

To a stirred solution of compound 6 (1 g, 1.62 mmol) in dioxane (5 mL),4 M HCl in dioxane (10 mL) was added at 0° C. and the reaction mixturewas stirred at room temperature for 2 h. The progress of the reactionwas monitored by TLC & LCMS. After complete consumption of compound 6,the solvent was removed under reduced pressure to obtain a cruderesidue, which was purified by Prep HPLC (Basic method) to obtainNRX-4010 (0.16 g, 19.1%) as a white solid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.85 (d, J=2.4 Hz, 1H), 8.32 (s, 2H), 8.14(d, J=7.4 Hz, 1H), 7.54 (t, J=7.4 Hz, 2H), 7.31 (d, J=8.1 Hz, 1H), 7.21(d, J=2.4 Hz, 1H), 7.15-6.92 (m, 4H), 4.72 (dd, J=11.4, 3.5 Hz, 1H),4.54-4.50 (m, 1H), 4.1-4.04 (m, 2H), 3.81 (p, J=6.3 Hz, 1H), 3.69 (dd,J=6.6, 4.3 Hz, 2H), 3.14 (dd, J=15.0, 5.1 Hz, 1H), 2.99 (dd, J=15.0, 9.1Hz, 1H), 2.44-2.42 (m, 1H), 1.84 (dd, J=13.6, 3.5 Hz, 1H), 1.68-1.56 (m,1H), 1.18 (d, J=6.3 Hz, 3H), 0.97 (d, J=6.3 Hz, 3H), 0.76-0.65 (m, 1H),0.63-0.59 (m, 1H).

HPLC purity: 97.68%

LCMS Calculated for C₂₅H₃₄N₆O₆: 514.25; Observed: 515.15[M+1]⁺.

G. Synthesis of NRX-4012:

Synthesis of(1S,3aR,6aS)-2-(tert-butoxycarbonyl)octahydrocyclopenta[c]pyrrole-1-carboxylicacid (2)

To a stirred solution of compound 1 (1.1 g, 7.09 mmol) and sodiumbicarbonate (1.18 g, 14.1 mmol) in water (20 mL), di-tertiary butyldicarbonate (2.25 g, 10.6 mmol) in dioxane (20 mL) was added and thereaction mixture was allowed to stir at room temperature for 12 h. Aftercompletion of the reaction as indicated by TLC, the reaction mixture wasquenched with water and extracted with ethyl acetate. The aqueous layerwas acidified by using 1N HCl to pH 2 and extracted with ethyl acetate.The organic layers were washed with brine, dried over anhydrous Na₂SO₄and concentrated under reduced pressure to obtain a crude residue, whichwas purified by column chromatography to afford compound 2 (1.3 g, 72%).

MS (ESI) m/z 256 [M+1]⁺

Synthesis of (1S,3aR,6aS)-tert-butyl1-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)hexahydrocyclopenta[c]pyrrole-2(1H)-carboxylate(4)

To a stirred solution of compound 2 (1.3 g, 5.07 mmol) in DCM (20 mL),HATU (2.89 g, 7.61 mmol) and diisopropylethylamine (2.65 mL, 15.2 mmol)were added. The solution was stirred at room temperature for 35 min,followed by compound 3 (1.54 g, 5.07 mmol and stirred at roomtemperature for 12 h. The progress of the reaction was monitored by TLC& LCMS. After complete consumption of starting material, the reactionwas quenched with water and extracted with DCM. The organic layers werewashed with brine, dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to obtain a crude residue, which was purified by columnchromatography to afford compound 4 (2.3 g, 83%).

LCMS: 442 (M−Boc)⁺.

Synthesis of(1S,3aR,6aS)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)octahydrocyclopenta[c]pyrrole-1-carboxamide(5)

To a stirred solution of compound 4 (2.2 g, 4.06 mmol) in dioxane (5mL), 4M HCl in dioxane (10 mL) was added at 0° C. and the reactionmixture was stirred at rt for 3 h. The progress of the reaction wasmonitored by TLC & LCMS. After complete consumption of compound 4, thesolvent was removed under reduced pressure to obtain a crude residue,which was purified by repeated washing with DCM to afford compound 5(1.65 g, 92%).

MS (ESI) m/z 442 [M+1]⁺.

Synthesis of tert-butyl((2S,3R)-1-41S,3aR,6aS)-1-(((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)carbamoyl)hexahydrocyclopenta[c]pyrrol-2(1H)-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(6)

To a stirred solution of(2S,3R)-2-((tert-butoxycarbonyl)amino)-3-hydroxybutanoic acid (1.6 g,3.62 mmol) in DCM (20 mL), HATU (2.06 g, 5.44 mmol) anddiisopropylethylamine (1.40 g, 10.8 mmol) were added. The solution wasstirred at room temperature for 35 min followed by compound 5 (0.79 g,3.62 mmol) was added and stirred at rt for 12 h. The progress of thereaction was monitored by TLC & LCMS. After complete consumption ofstarting material, the reaction was quenched with water and extractedwith DCM. The organic layers were washed with sodium bicarbonatesolution and brine, dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to obtain a crude residue, which was purified by columnchromatography to afford compound 6 (1.8 g, 77.5%).

MS (ESI) m/z: 543 [M−Boc]⁺.

Synthesis of(1S,3aR,6aS)—N—((S)-1-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)amino)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-2-((2S,3R)-2-amino-3-hydroxybutanoyl)octahydrocyclopenta[c]pyrrole-1-carboxamide(NRX-4012)

To a stirred solution of compound 6 (0.65 g, 1.01 mmol) in dioxane (5mL), 4 M HCl in dioxane (10 mL) was added at 0° C. and the reactionmixture was stirred at rt for 3 h.

The progress of the reaction was monitored by TLC & LCMS. After completeconsumption of compound 6, the solvent was removed under reducedpressure to obtain a crude residue, which was purified by Prep HPLC(Basic method) to obtain compound NRX-4012 (0.19 g, 35%) as an off-whitesolid.

¹H NMR (400 MHz, DMSO-d₆) δ: 10.88-10.81 (m, 1H), 8.36 (s, 2H), 8.17 (d,J=7.3 Hz, 1H), 7.61-7.51 (m, 2H), 7.31 (d, J=8.1 Hz, 1H), 7.20 (d, J=2.4Hz, 1H), 7.17-6.92 (m, 5H), 4.51 (td, J=8.2, 5.0 Hz, 1H), 4.22-4.09 (m,1H), 4.09-3.98 (m, 2H), 3.73-3.38 (m, 3H), 3.31-3.13 (m, 1H), 3.11-2.97(m, 1H), 1.85-1.33 (m, 6H), 1.10-0.94 (m, 6H).

HPLC purity: 95.3%

LCMS Calculated for C₂₇H₃₈N₆O₆: 542.64; Observed: 543.55 [M+1]⁺.

Example 4—Synthesis of Compounds of Formula (V)

A. Synthesis of NRX-1001 & 1002:

Synthesis of Methyl D-Prolinate Hydrochloride (1)

To a stirred solution of D-proline (SM) (20 g, 173.9 mmol) in methanol(200 mL) was added thionyl chloride (16 mL, 208.4 mmol) drop wise at 0°C. under argon atmosphere. The reaction mixture was allowed to stir at80° C. for 8 h. After consumption of the starting material (by TLC),reaction mixture was brought to RT and volatiles were evaporated underreduced pressure. Obtained residue was triturated with ether to affordcompound 1 (21.5 g, 75%) as thick syrup.

¹H-NMR: (500 MHz, DMSO-d₆): δ 9.10 (s, 1H), 4.34-4.24 (m, 1H), 3.75 (s,3H), 3.20-3.16 (m, 2H), 2.27-2.21 (m, 2H), 2.01-1.87 (m, 2H).

Synthesis of benzyl(S)-2-((R)-2-(methoxycarbonyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(2)

To a stirring solution of compound 1 (1 g, 6.06 mmol) in DCM (50 mL)were added and DIPEA (3.2 ml, 18.18 mmol), DCC (1.8 g, 9.09 mmol) andInt-B (1.88 g, 7.27 mmol) at 0° C. under argon atmosphere. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(20 mL) and extracted with DCM (3×50 mL). Combined organic layers weredried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 2% MeOH/DCM to obtain compound 2 (1 g, 47%) as thick syrup.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.37-7.28 (m, 5H), 5.11-5.00 (m, 2H),4.57-4.51 (m, 1H), 4.27-4.23 (m, 1H), 3.65 (s, 3H), 3.47-3.36 (m, 4H),2.21-2.08 (m, 2H), 1.95-1.70 (m, 4H), 1.27-1.09 (m, 2H).

LCMS (m/z): 361.4 [M⁺+1]

Synthesis of ((benzyloxy)carbonyl)-L-prolyl-D-proline (3)

To a stirring solution of compound 2 (1 g, 2.7 mmol) in THF:H₂O (10 mL,1:1) was added LiOH (232 mg, 5.5 mmol) at 0° C. The reaction mixture wasbrought to RT and stirred for 18 h. After consumption of the startingmaterial (by TLC), volatiles were evaporated under reduced pressure. Theresidue was diluted with water (20 mL), pH was adjusted to 2 with citricacid and extracted with EtOAc (2×30 mL). Combined organic layer wasdried over Na₂SO₄ and concentrated to afford compound 3 (800 mg, 83%) assticky solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 12.45 (br s, 1H), 7.31-7.27 (m, 5H),5.12-5.00 (m, 2H), 4.25-4.17 (m, 2H), 3.46-3.17 (m, 4H), 2.19-2.08 (m,2H), 1.85-1.72 (m, 6H).

LCMS (m/z): 347.4 [M⁺+1]

Synthesis of benzyl(S)-2-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(4)

To a stirring solution of compound 3 (700 mg, 2.01 mmol) in DCM (15 mL)was added DIPEA (1.1 mL, 6.05 mmol), EDCI (577 mg, 3.02 mmol) and HOBt(408 mg, 3.02 mmol) at 0° C. under argon atmosphere. The reactionmixture was stirred at RT for 10 minutes. Then Int-A (285 g, 2.4 mmol)in DMF (10 mL) was added at 0° C. and allowed to stir at RT for 18 h.The reaction mixture was brought to RT and stirred for 16 h. Afterconsumption of the starting material (by TLC), the reaction mixture wasdiluted with water (10 mL) and extracted with DCM (3×20 mL). Combinedorganic layers were dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to afford crude compound which was purified by columnchromatography by eluting with 2% MeOH/DCM to obtain compound 4 (630 mg,70%) as off white solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 8.01-7.95 (dd, J=23.0, 8.5 Hz, 1H),7.41-7.28 (m, 5H), 5.12-4.99 (m, 2H), 4.90-4.81 (m, 2H), 4.59-4.45 (m,2H), 4.18-4.06 (m, 2H), 3.52-3.38 (m, 4H), 2.01-1.67 (m, 9H), 1.04-1.00(m, 3H).

LCMS (m/z): 447.5 [M⁺+1]

Synthesis of(R)-1-(L-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1001)

To a stirring solution of compound 4 (570 mg, 1.27 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (150 mg) at RT and stirred for 12 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite, filtrate wasconcentrated under reduced pressure and dried under vacuum to affordNRX-1001 (300 mg, 75%) an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.61-4.57 (m, 1H), 4.46-4.39 (m, 2H),4.10-4.07 (m, 1H), 3.85-3.70 (m, 2H), 3.19-3.13 (m, 1H), 2.97-2.91 (m,1H), 2.43-2.30 (m, 2H), 2.17-2.02 (m, 3H), 1.95-1.78 (m, 3H), 1.27-1.30(m, 3H).

LCMS (ESI): m/z 313.3 [M⁺+1]

UPLC: 95.36%

Synthesis of benzyl((2S,3R)-1-((S)-2-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1001 (200 mg, 0.64 mmol) in DCM (10 mL)was added DIPEA (0.35 mL, 1.92 mmol), HATU (243 mg, 0.64 mmol) and Int C(194 mg, 0.76 mmol) and at 0° C. under argon atmosphere. The reactionmixture was brought to RT and stirred for 18 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(10 mL) and extracted with 10% MeOH/DCM (3×20 mL). Combined organiclayers were dried over anhydrous Na₂SO₄ and concentrated under reducedpressure to afford crude compound which was purified by columnchromatography by eluting with 3% MeOH/DCM to obtain compound 5 (260 mg,74%) as an off white solid.

¹H-NMR: (400 MHz, CD₃OD): δ 7.35-7.29 (m, 5H), 5.08 (s, 2H), 4.95-4.93(m, 1H), 4.54-4.52 (m, 1H), 4.36-4.30 (m, 2H), 4.21-4.20 (m, 1H),3.98-3.94 (m, 2H), 3.76-3.67 (m, 2H), 3.64-3.54 (m, 1H), 2.10-2.05 (m,2H), 1.38-1.35 (m, 6H), 1.28-1.26 (m, 3H), 1.17-1.14 (m, 3H).

LCMS (m/z): 548.6 [M⁺+1]

Synthesis of(R)-1-(L-threonyl-L-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1002)

To a stirring solution of compound 5 (260 mg, 0.47 mmol) in methanol (5mL) was added 50% wet 10% Pd/C (100 mg) at RT and stirred for 2 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas dried over anhydrous Na₂SO₄ and concentrated under reduced pressureto afford crude compound which was purified by column chromatography byeluting with 1% aq.NH₃ in 15% MeOH/DCM to obtain NRX-1002 (80 mg, 40%)as a white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.64-4.55 (m, 2H), 4.41-4.26 (m, 2H),3.99-3.59 (m, 6H), 2.56-2.27 (m, 2H), 2.22-2.16 (m, 6H), 1.30-1.22 (m,6H).

LCMS (ESI): m/z 414.5 [M⁺+1]

UPLC 94.94%

B. Synthesis of NRX-1015 & 1016:

Synthesis of benzyl(S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1)

To a stirring solution of compound (SM) (4 g, 16.1 mmol) in DMF (50 mL)was added DIPEA (8.4 mL, 48.2 mmol), EDCI (4.6 g, 24.07 mmol), HOBt(3.24 g, 22.1 mmol) at 0° C. under argon atmosphere. After stirred for10 minutes, Int A (2.2 g, 19.2 mmol) was added.

The reaction mixture was brought to RT and stirred for 16 h. Afterconsumption of the starting material (by TLC), the reaction mixture wasdiluted with EtOAc (20 mL) and washed with brine solution (2×20 mL).Organic layer was dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to afford crude compound which was purified by columnchromatography by eluting with 2% MeOH/DCM to obtain compound 1 (4.5 g,80%) as white solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.68-7.60 (m, 1H), 7.36-7.29 (m, 5H),7.08-7.06 (m, 2H), 5.11-4.95 (m, 2H), 4.82-4.81 (m, 1H), 4.38-4.29 (m,1H), 4.16-3.97 (m, 2H), 3.44-3.31 (m, 2H), 2.19-2.10 (m, 1H), 1.88-1.79(m, 3H), 1.03-0.91 (m, 3H).

LCMS (m/z): 350.3 [M⁺+1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(2)

To a stirring solution of compound 1 (2.3 g, 6.5 mmol) in methanol (50mL) was added 50% wet 10% Pd/C (800 mg) at RT and stirred for 2 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Obtained filtrate wasconcentrated under reduced pressure and dried under vacuum to affordcompound 2 (1.2 g, 85%) as semi solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 8.10 (d, J=9.0 Hz, 1H), 7.20-7.16 (m, 2H),4.91 (d, J=4.5 Hz, 1H), 4.07-4.02 (m, 2H), 3.59-3.56 (m, 1H), 2.92-2.87(m, 2H), 2.78-2.73 (m, 1H), 1.97-1.91 (m, 1H), 1.70-1.57 (m, 3H),1.00-0.95 (m, 3H).

LCMS (ESI): m/z 216.0 [M⁺+1]

Synthesis of tert-butyl(S)-3-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of compound 2 (125 mg, 0.58 mmol) in DMF (1.5 mL)was added DIPEA (0.3 mL, 1.74 mmol), HATU (220 mg, 0.58 mmol) and Int B(124 mg, 0.58 mmol) at 0° C. under argon atmosphere. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(10 mL) and extracted with 5% MeOH/DCM (2×50 mL). Combined organiclayers were dried over anhydrous Na₂SO₄ and concentrated under reducedpressure to afford crude compound which was purified by columnchromatography by eluting with 5% MeOH/DCM to obtain compound 3 (160 mg,66%) as sticky material.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.54-7.47 (m, 1H), 7.06 (s, 2H), 4.91-4.80(m, 2H), 4.16-3.98 (m, 2H), 3.62-3.42 (m, 3H), 3.36-3.32 (m, 1H),3.16-3.13 (m, 2H), 3.08-3.01 (m, 1H), 2.06-2.04 (m, 2H), 1.89-1.78 (m,4H), 1.39 (s, 9H), 1.04-1.01 (m, 3H).

LCMS (m/z): 411.3 [M⁺−1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((S)-pyrrolidine-3-carbonyl)pyrrolidine-2-carboxamide(NRX-1015)

To a solution of compound 3 (630 mg, 1.53 mmol) in DCM (5 mL) was added4N HCl in dioxane (1.1 mL, 4.59 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 4 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure. Obtained crude was triturated with methyltertiary-butyl ether (2×10 mL) and dried under vacuum to afford NRX-1015(532 mg, 95%) as an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.59-4.56 (m, 1H), 4.39-4.36 (m, 1H),4.34-4.32 (m, 1H), 3.83-3.78 (m, 2H), 3.68-3.64 (m, 1H), 3.61-3.56 (m,2H), 3.54-3.46 (m, 2H), 2.54-2.37 (m, 2H), 2.23-2.03 (m, 4H), 1.30 (t,J=6.0 Hz, 3H).

LCMS (ESI): m/z 313.5 [M⁺+1]

UPLC: 94.13%

Synthesis of benzyl((2S,3R)-1-((S)-3-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilyl)oxy)-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1015 (300 mg, 0.86 mmol) in DMF (3 mL) wasadded DIPEA (0.45 mL, 2.58 mmol) and Int D (479 mg, 1.03 mmol) at 0° C.under argon atmosphere. The reaction mixture was brought to RT andstirred for 4 h. After consumption of the starting material (by TLC),the reaction mixture was diluted with water (5 mL) and extracted withEtOAc (2×10 mL). Combined organic layers were dried over anhydrousNa₂SO₄ and concentrated under reduced pressure to afford crude compoundwhich was purified by column chromatography by eluting with 3% MeOH/DCMto obtain compound 5 (400 mg, 70%) as sticky liquid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.94-7.89 (m, 1H), 7.56-7.50 (m, 1H),7.34-7.26 (m, 5H), 7.06 (s, 2H), 4.79 (s, 2H), 4.69-4.65 (m, 1H),4.40-4.38 (m, 1H), 4.26-4.22 (m, 2H), 4.07-4.03 (m, 2H), 3.93-3.87 (m,1H), 3.66-3.86 (m, 2H), 3.39-3.34 (m, 3H), 3.19-3.09 (m, 1H), 2.23-2.07(m, 2H), 1.94-1.79 (m, 4H), 1.08-1.02 (m, 6H), 0.81 (s, 9H), 0.06-0.01(m, 6H).

LCMS (ESI): m/z 662.8 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((S)-3-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(6)

To a stirring solution of compound 5 (400 mg, 0.61 mmol) in THF (2 mL)was added TBAF (189 mg, 0.72 mmol) at 0° C. under argon atmosphere. Thereaction mixture was brought to RT and stirred for 4 h. Afterconsumption of the starting material (by TLC), the reaction mixture wasdiluted with water (5 mL) and extracted with 10% MeOH/DCM (2×10 mL).Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 4% MeOH/DCM to obtaincompound 6 (200 mg, 60%) as off white solid.

¹H-NMR: (400 MHz, D₂O): δ 7.44 (s, 5H), 5.15 (s, 2H), 4.52-4.48 (m, 1H),4.37-4.28 (m, 2H), 4.09-3.97 (m, 1H), 3.76-3.46 (m, 8H), 2.34-2.32 (m,2H), 2.05-1.92 (m, 4H), 0.97-0.93 (m, 6H).

LCMS (ESI): m/z 548.6 [M⁺+1]

Synthesis of(S)-1-((S)-1-(L-threonyl)pyrrolidine-3-carbonyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1016)

To a stirring solution of compound 6 (700 mg, 1.28 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (300 mg) at RT and stirred for 4 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Obtained filtrate wasconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 15% MeOH/DCM+1 mLaq.NH₃ to obtain NRX-1016 (250 mg, 47%) as an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.89-4.85 (m, 1H), 4.58-4.55 (m, 1H),4.42-4.33 (m, 2H), 4.02-3.97 (m, 1H), 3.86-3.53 (m, 7H), 2.45-2.33 (m,2H), 2.22-2.01 (m, 4H), 1.30-1.26 (m, 6H).

LCMS (ESI): m/z 414.5 [M+⁺1]

UPLC: 95.15%

C. Synthesis of NRX-1005 & 1006:

Synthesis of methyl L-prolinate (1)

To a stirred solution of L-proline (SM) (25 g, 217.3 mmol) in methanol(10 mL) was added thionyl chloride (19 mL, 260.8 mmol) drop wise at 0°C. under argon atmosphere. The reaction mixture was allowed to stir at70° C. for 16 h. After consumption of the starting material (by TLC),reaction mixture was brought to RT and volatiles were evaporated underreduced pressure to afford compound 1 (35 g, 98%) as yellow color syrup.

¹H-NMR: (500 MHz, DMSO-d₆): δ 9.09 (s, 1H), 4.35-4.24 (m, 1H), 3.75 (s,3H), 3.21-3.16 (m, 2H), 2.28-2.21 (m, 2H), 2.01-1.88 (m, 2H).

LCMS (m/z): 130.1 [M⁺+1]

Synthesis of benzyl(R)-2-((S)-2-(methoxycarbonyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(2)

To a stirring solution of compound 1 (5 g, 20.07 mmol) in DCM (50 mL)were added Int B (4.98 g, 30.1 mmol), DCC (6.21 g, 30.1 mmol) and DMPP(245 mg, 2.01 mmol) at 0° C. under argon atmosphere. The reactionmixture was stirred at RT for 10 minutes. Then DIPEA (6.97 mL, 40.1mmol) was added at 0° C. and allowed to stir at RT for 16 h. Afterconsumption of the starting material (by TLC), the reaction mixture wasdiluted with water (20 mL) and extracted with DCM (3×50 mL). Combinedorganic layers were dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to afford crude compound which was purified by columnchromatography by eluting with 50% EtOAc/n-hexane to obtain compound 2(5 g, 69%) as brown solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.53-7.27 (m, 5H), 5.10-5.00 (m, 1H),4.56-4.52 (m, 1H), 4.26-4.24 (m, 1H), 3.72-3.69 (m, 1H), 3.64 (s, 3H),3.46-3.36 (m, 4H), 2.20-2.09 (m, 2H), 1.95-1.82 (m, 6H).

LCMS (m/z): 361.3 [M⁺+1]

Synthesis of ((benzyloxy)carbonyl)-D-prolyl-L-proline (3)

To a stirring solution of compound 2 (400 mg, 1.11 mmol) in THF:H₂O (10mL, 1:1) was added LiOH.H₂O (140 mg, 3.33 mmol) at 0° C. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), volatiles were evaporated under reducedpressure, washed with 1N HCl and extracted with DCM (2×20 mL). Combinedorganic layer was dried over Na₂SO₄ and concentrated to afford compound3 (240 mg, 63%) as white color sticky solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 12.82 (br s, 1H), 7.36-7.26 (m, 5H),5.12-5.01 (m, 2H), 4.24-4.15 (m, 2H), 3.42-3.16 (m, 4H), 2.19-2.08 (m,6H), 1.60-1.52 (m, 2H).

LCMS (m/z): 347.3 [M⁺+1]

Synthesis of benzyl(R)-2-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(4)

To a stirring solution of compound 3 (3 g, 8.6 mmol) in DMF (15 mL) wasadded Int A (1.22 g, 10.4 mmol), EDCI (2.48 g, 12.9 mmol), HOBt (1.75 g,12.9 mmol) and DIPEA (4.65 mL, 25.8 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 16 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (15 mL) and extracted with DCM (3×50 mL).Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 50% EtOAc/hexane toobtain compound 4 (2.9 g, 75%) as off white sticky solid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.91-7.88 (dd, J=13.6, 8.8 Hz, 0.5H),7.39-7.27 (m, 5H), 5.19-5.01 (m, 2H), 5.12-5.03 (m, 1H), 4.97-4.83 (m,2H), 4.68-4.51 (m, 1H), 4.36-4.26 (m, 1H), 4.14-3.94 (m, 1.5H),3.89-3.82 (m, 1H), 3.56-3.53 (m, 0.5H), 3.45-3.37 (m, 3H), 3.24-3.20 (m,0.5H), 1.98-1.67 (m, 8H), 1.04-1.00 (m, 3H).

LCMS (m/z): 447.6 [M⁺+1]

Synthesis of(S)-1-(D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1005)

To a stirring solution of compound 4 (700 mg, 1.56 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (100 mg) at RT and stirred for 16 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Obtained filtrate wasconcentrated under reduced pressure and dried under vacuum to affordNRX-1005 (400 mg, 81%) as white color solid.

¹H-NMR: (500 MHz, D₂O): δ 4.55-4.52 (m, 1H), 4.37-4.30 (m, 2H),4.09-4.06 (m, 1H), 3.83-3.78 (m, 1H), 3.71-3.62 (m, 1H), 3.16-3.11 (m,1H), 2.94-2.89 (m, 1H), 2.40-2.27 (m, 2H), 2.10-2.01 (m, 3H), 1.94-1.76(m, 3H), 1.28 (t, J=5.2 Hz, 3H).

LCMS (ESI): m/z 313.3 [M⁺+1]

UPLC: 99.67%

Synthesis of benzyl((2S,3R)-1-((R)-2-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1005 (400 mg, 1.28 mmol) in DMF (8 mL) wasadded HATU (487 mg, 1.28 mmol) and Int C (356 mg, 1.41 mmol) and DIPEA(0.44 mL, 2.56 mmol) at 0° C. under argon atmosphere. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(10 mL) and extracted with DCM (2×20 mL) and 10% MeOH/DCM (2×20 mL).Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 7% MeOH/DCM to obtaincompound 5 (250 mg, 35%) as brown sticky solid.

¹H-NMR: (400 MHz, D₂O): δ 7.53-7.51 (m, 5H), 5.27-5.19 (m, 2H),4.57-4.51 (m, 2H), 4.43-4.29 (m, 2H), 4.24-4.18 (m, 1H), 4.13-4.05 (m,1H), 3.85-3.77 (m, 3H), 3.63-3.57 (m, 1H), 2.44-2.41 (m, 2H), 2.17-2.01(m, 6H), 1.28-1.26 (m, 6H).

LCMS (m/z): 548.6 [M⁺+1]

Synthesis of(S)-1-(L-threonyl-D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1006)

To a stirring solution of compound 5 (250 mg, 0.45 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (80 mg) at RT and stirred for 16 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Organic layer wasdried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 15% MeOH/DCM+1 mL aq.NH₃ to obtain to afford NRX-1006 (65mg, 34%) as white color solid.

¹H-NMR: (400 MHz, D₂O): δ 4.55-4.53 (m, 1H), 4.40-4.37 (m, 2H),4.06-3.95 (m, 2H), 3.89-3.72 (m, 4H), 3.62-3.61 (m, 1H), 2.42-2.35 (m,2H), 2.15-1.98 (m, 6H), 1.28-1.26 (m, 6H).

LCMS (ESI): m/z 414.5 [M⁺+1]

UPLC: 95.41%

D. Synthesis of NRX-1009 & 1010:

Synthesis of tert-butyl(R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1)

To a stirring solution of(R)-1-(tert-butoxycarbonyl)pyrrolidine-3-carboxylic acid (SM) (1 g, 5.05mmol) in DMF (10 mL) was added HATU (2.88 g, 7.5 mmol), Int A (596 mg,5.05 mmol) and DIPEA (1.75 mL, 10.1 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 16 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (10 mL) and extracted with DCM (2×50 mL).Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 7% MeOH/DCM to obtaincompound 1 (0.92 g, 58%) as white color syrup.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.73 (d, J=9.0 Hz, 1H), 7.19 (s, 1H), 7.04(s, 1H), 4.81 (d, J=5.5 Hz, 1H), 4.14-4.11 (dd, J=9.5, 3.5 Hz, 1H),4.00-3.97 (dd, J=9.5, 5.5 Hz, 1H), 3.47-3.43 (m, 1H), 3.31 (s, 1H),3.25-3.08 (m, 3H), 1.98-1.96 (m, 2H), 1.39 (s, 9H), 1.01 (t, J=7.0 Hz,3H).

LCMS (m/z): 314.3 [M⁺−1]

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(2)

To a solution of compound 1 (200 mg, 0.63 mmol) in DCM (5 mL) was added4M HCl in dioxane (0.11 mL, 3.17 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 4 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure. Obtained crude was washed with hexanes (2×10 mL)and dried under vacuum to afford compound 2 (130 mg, 81%) as white colorsolid.

¹H-NMR: (400 MHz, D₂O): δ 4.38-4.21 (m, 2H), 3.60-4.48 (m, 2H),3.47-3.37 (m, 3H), 2.48-2.38 (m, 1H), 2.31-2.16 (m, 1H), 1.26 (t, J=6.4Hz, 3H).

LCMS (ESI): m/z 216.0 [M⁺+1]

Synthesis of benzyl(S)-2-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of Int C (4.2 g, 15.7 mmol) in DMF (15 mL) wasadded DIPEA (3.17 mL, 18.2 mmol) and compound 2 (2.3 g, 9.1 mmol) at 0°C. under argon atmosphere. The reaction mixture was brought to RT andstirred for 16 h. After consumption of the starting material (by TLC),the reaction mixture was diluted with water (10 mL) and extracted withDCM (2×50 mL) and 10% MeOH/DCM. Combined organic layers were dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 7%MeOH/DCM to obtain compound 3 (1.1 g, 27%) as brown color solid.

¹H-NMR: (400 MHz, D₂O): δ 7.56-7.41 (m, 5H), 5.23-5.17 (m, 1H),5.07-5.04 (m, 1H), 4.64-4.61 (m, 1H), 4.42-4.27 (m, 2H), 3.85-3.72 (m,1H), 3.63-3.58 (m, 2H), 3.54-3.40 (m, 2H), 3.35-3.25 (m, 1H), 2.39-2.29(m, 1H), 2.18-1.90 (m, 3H), 1.42-1.39 (m, 3H), 1.30-1.24 (m, 3H).

LCMS (m/z): 447.4 [M⁺+1]

Synthesis of(R)-1-(L-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1009)

To a stirring solution of compound 3 (1.1 g, 2.46 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (200 mg) at RT and stirred for 16 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Obtained filtrate wasconcentrated under reduced pressure and dried under vacuum to affordNRX-1009 (605 mg, 78%) as white color solid.

¹H-NMR: (400 MHz, D₂O): δ 4.3-4.33 (m, 1H), 4.28-4.25 (m, 1H), 4.20-4.17(m, 1H), 3.81-3.24 (m, 6H), 3.09-3.05 (m, 1H), 2.39-2.08 (m, 3H),2.05-1.79 (m, 3H), 1.26-1.23 (m, 3H).

LCMS (ESI): m/z 313.5 [M⁺+1]

HPLC: 98.64%

Synthesis of benzyl((2S,3R)-1-((S)-2-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(4)

To a stirring solution of NRX-1009 (200 mg, 0.64 mmol) in DMF (3 mL) wasadded HATU (244 mg, 0.64 mmol), Int D (178 mg, 0.7 mmol) and DIPEA (0.22mL, 1.28 mmol) at 0° C. under argon atmosphere. The reaction mixture wasbrought to RT and stirred for 16 h. After consumption of the startingmaterial (by TLC), the reaction mixture was diluted with water (10 mL)and extracted with 10% MeOH/DCM (2×20 mL). Combined organic layers weredried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 7% MeOH/DCM to obtain compound 4 (190 mg, 54%) as brownsolid.

¹H-NMR: (400 MHz, D₂O): δ 7.50-7.48 (m, 5H), 5.26-5.18 (m, 2H),4.71-4.67 (m, 1H), 4.43-4.29 (m, 3H), 4.13-4.09 (m, 1H), 3.80-3.75 (m,2H), 3.62-3.59 (m, 2H), 3.48-3.44 (m, 3H), 3.36-3.24 (m, 1H), 2.43-2.38(m, 1H), 2.32-2.25 (m, 1H), 2.13 (s, 1H), 2.14-1.95 (m, 2H), 1.41-1.31(m, 3H), 1.29-1.25 (m, 3H).

LCMS (m/z): 548.5 [M⁺+1]

Synthesis of(R)-1-(L-threonyl-L-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1010)

To a stirring solution of compound 4 (185 mg, 0.33 mmol) in methanol (5mL) was added 50% wet 10% Pd/C (90 mg) at RT and stirred for 16 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Organic layer wasdried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 1% aq.NH₃ in 10% MeOH/DCM to obtain to afford NRX-1010 (55mg, 39%) as off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.81-4.70 (m, 1H), 4.40-4.37 (m, 1H),4.31-4.28 (m, 1H), 3.99-3.33 (m, 9H), 4.45-34.25 (m, 3H), 2.18-2.04 (m,2H), 2.02-1.89 (m, 1H), 1.33-1.26 (m, 6H).

LCMS (ESI): m/z 414.6 [M⁺+1]

UPLC: 98.16%

E. Synthesis of NRX-1003 & 1004:

Synthesis of methyl D-prolinate hydrochloride (1)

To a stirred suspension of D-proline (SM) (10 g, 86.9 mmol) in methanol(100 mL) was added thionyl chloride (7.6 mL, 104.3 mmol) drop wise at 0°C. under nitrogen atmosphere. The reaction mixture was heated to refluxfor 16 h. After consumption of the starting material (by TLC), reactionmixture was brought to RT, volatiles were concentrated under vacuum andthe crude was triturated with n-hexane to afford compound 1 ashydrochloride salt (10.5 g, 93%) as brown syrup.

¹H-NMR: (400 MHz, DMSO-d₆): δ 10.32-10.14 (d, 1H), 9.05-8.74 (d, 1H),3.97-3.78 (m, 1H), 3.75 (s, 3H), 3.21-3.16 (m, 2H), 2.30-2.21 (m, 1H),1.99-1.87 (m, 3H).

LCMS (m/z): 144.2 [M⁺+1]

Synthesis of benzyl(R)-2-((R)-2-(methoxycarbonyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(2)

To a stirring solution of compound 1 (5 g, 38.4 mmol) in DCM (50 mL)were added DIPEA (20 mL, 115.2 mmol), DCC (11.9 g, 57.6 mmol) and Int-A(11.5 g, 46.1 mmol) at 0° C. under nitrogen atmosphere. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), brought to RT and filtered through cottonbed. The reaction was diluted with water (50 mL) and extracted withCH₂Cl₂ (3×30 mL). The organic layer was dried over Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 20% EtOAC/n-hexane toobtain compound 2 (6.1 g, 44%) as syrup.

¹H-NMR: (500 MHz, D₂O): δ 7.34-7.25 (m, 5H), 5.04 (s, 2H), 4.88-3.86 (m,1H), 4.54-4.52 (m, 1H), 3.62 (s, 3H), 3.44-3.34 (m, 4H), 1.93-1.78 (m,8H).

LCMS (ESI): m/z 144.1 [(M⁺+1)-Boc]

Synthesis of ((benzyloxy)carbonyl)-D-prolyl-D-proline (3)

To a stirring solution of compound 2 (6.1 g, 16.9 mmol) in THF:H₂O (60mL, 1:1) were added lithium hydroxide (1.77 g, 42.3 mmol) at 0° C. Thereaction mixture was brought to RT and stirred for 16 h. Afterconsumption of the starting material (by TLC), the reaction wasextracted with DCM (3×30 mL). The combined organic layers were driedover Na₂SO₄ and concentrated to obtain crude compound which was washedwith hexane to afford compound 3 (3.2 g, crude) as an off white solid.

¹H-NMR: (500 MHz, D₂O): δ 7.48-7.40 (m, 5H), 5.18 (s, 2H), 4.66-3.64 (m,1H), 4.13-4.11 (m, 1H), 3.57-3.45 (m, 4H), 2.12-1.90 (m, 8H).

LCMS (ESI): m/z 242.2 [M⁺+1];

Synthesis of benzyl(R)-2-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(4)

To a stirring solution of compound 3 (3 g, 8.6 mmol) in DCM (30 mL) wereadded, DIPEA (4.6 mL, 25.8 mmol), EDCI.HCl (2.47 g, 12.9 mmol) and HOBt(6.7 mL, 38.4 mmol) at 0° C. under nitrogen atmosphere. A solution ofInt-B (1.2 g, 10.3 mmol) in DMF (10 mL) was added to the reactionmixture and allowed to stir at RT for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(50 mL) and extracted with DCM (3×30 mL). Separated organic layer wasdried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 5% MeOH-DCM to obtain compound 4 (3 g, 77%) as an off whitesolid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.81-7.80 (d, 1H), 7.37-7.26 (m, 5H),5.09-5.00 (m, 2H), 4.91-4.82 (m, 2H), 4.54-4.42 (m, 2H), 4.14 (s, 1H),3.97-3.96 (m, 1H), 3.53-3.36 (m, 4H), 2.19-2.15 (m, 1H), 1.98-1.90 (m,1H), 1.85-1.76 (m, 6H), 1.64-1.58 (m, 1H), 1.05-1.01 (m, 3H).

LCMS (ESI): m/z 242.2 [M⁺+1];

Synthesis of(R)-1-(D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1003)

To a stirring solution of compound 4 (1 g, 2.2 mmol) in methanol (20 mL)was added 50% wet 10% Pd/C (400 mg) at RT and stirred for 16 h under H₂atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the pad waswashed with methanol (50 mL). Obtained filtrate was concentrated underreduced pressure to afford NRX-1003 (550 mg, 78%) as white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.67-4.59 (m, 1H), 4.43-4.37 (m, 2H),4.10-4.08 (m, 1H), 3.82-3.78 (m, 1H), 3.71-3.65 (m, 1H), 3.13-3.09 (m,1H), 2.93-2.91 (m, 1H), 2.43-2.32 (m, 2H), 2.15-1.99 (m, 3H), 1.91-1.79(m, 3H), 1.26-1.24 (m, 3H).

LCMS (ESI): m/z 258.9 [M⁺]

Synthesis of benzyl((2S,3R)-1-((R)-2-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1003 (600 mg, 1.98 mmol) in DCM (6 mL)were added DIPEA (1 mL, 5.7 mmol), HATU (730 mg, 1.98 mmol) and Int C(583 mg, 2.3 mmol) at 0° C. under nitrogen atmosphere. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(15 mL) and extracted with 15% MeOH-DCM solvent mixture (3×20 mL).Separated organic layer was dried over anhydrous Na₂SO₄ and concentratedunder reduced pressure to afford crude compound which was purified bycolumn chromatography by eluting with 5% MeOH-DCM to obtain compound 5(510 mg, 51%) as white solid.

¹H-NMR: (500 MHz, D₂O): δ 7.48 (s, 5H), 5.19 (s, 2H), 4.59-4.57 (m, 2H),4.51-4.41 (m, 2H), 4.17-4.15 (m, 2H), 3.78-3.70 (m, 4H), 2.13-1.96 (m,4H), 1.51-1.32 (m, 4H), 1.24-1.22 (m, 6H).

LCMS (ESI): m/z 477.4 [M⁺+1]

Synthesis of(R)-1-(L-threonyl-D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1004)

To a stirring solution of compound 5 (500 mg, 0.91 mmol) in methanol (5mL) was added 50% wet 10% Pd/C (500 mg) at RT under nitrogen atmosphere.The reaction mixture was stirred RT for 16 h under H₂ atmosphere. Afterconsumption of the starting material (by TLC), the reaction mixture wasfiltered through a pad of celite and the pad was washed with MeOH (20mL). Obtained filtrate was concentrated under reduced pressure to affordcrude compound which was purified by column chromatography by elutingwith 15% MeOH-DCM to obtain NRX-1004 (75 mg, 20%) as white solid. Theracemic was separated by chiral HPLC purification.

¹H-NMR: (400 MHz, D₂O): δ 4.31-4.28 (m, 2H), 4.12-4.06 (m, 1H),4.00-3.94 (m, 3H), 3.64 (s, 2H), 3.59-3.52 (m, 1H), 3.41-3.34 (m, 1H),2.02-1.93 (m, 4H), 1.30 (d, J=5.6 Hz, 3H),

1.23 (d, J=6.4 Hz, 3H)

LCMS (ESI): m/z 343.4 [M⁺+1];

HPLC: 96.77%

F. Synthesis of NRX-1011 & 1012:

Synthesis of tert-butyl(R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1)

To a stirring solution of(R)-1-(tert-butoxycarbonyl)pyrrolidine-3-carboxylic acid (SM) (1 g, 5.05mmol) in DMF (10 mL) was added HATU (2.88 g, 7.5 mmol), Int A (596 mg,5.05 mmol) and DIPEA (1.75 mL, 10.1 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 16 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (10 mL) and extracted with DCM (2×50 mL).Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 7% MeOH/DCM to obtaincompound 1 (0.92 g, 58%) as white color syrup.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.73 (d, J=9.0 Hz, 1H), 7.19 (s, 1H), 7.04(s, 1H), 4.81 (d, J=5.5 Hz, 1H), 4.14-4.11 (dd, J=9.5, 3.5 Hz, 1H),4.00-3.97 (dd, J=9.5, 5.5 Hz, 1H), 3.47-3.43 (m, 1H), 3.31 (s, 1H),3.25-3.08 (m, 3H), 1.98-1.96 (m, 2H), 1.39 (s, 9H), 1.01 (t, J=7.0 Hz,3H).

LCMS (m/z): 314.3 [M⁺−1]

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(2)

To a solution of compound 1 (200 mg, 0.63 mmol) in DCM (5 mL) was added4M HCl in dioxane (0.11 mL, 3.17 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 4 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure. Obtained crude was washed with hexanes (2×10 mL)and dried under vacuum to afford compound 2 (130 mg, 81%) as white colorsolid.

¹H-NMR: (400 MHz, D₂O): δ 4.38-4.21 (m, 2H), 3.60-4.48 (m, 2H),3.47-3.37 (m, 3H), 2.48-2.38 (m, 1H), 2.31-2.16 (m, 1H), 1.26 (t, J=6.4Hz, 3H).

LCMS (ESI): m/z 216.0 [M⁺+1]

Synthesis of benzyl(R)-2-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of compound 2 (950 mg, 3.77 mmol) in DMF (5 mL)was added Int C (1.71 g, 6.42 mmol) and DIPEA (1.31 mL, 7.55 mmol) andat 0° C. under argon atmosphere. The reaction mixture was brought to RTand stirred for 16 h. After consumption of the starting material (byTLC), the reaction mixture was diluted with water (5 mL) and extractedwith 10% MeOH/DCM (2×10 mL). Combined organic layers were dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 6%MeOH/DCM to obtain compound 3 (510 mg, 30%) as brown color solid.

¹H-NMR: (500 MHz, D₂O): δ 7.51-7.40 (m, 5H), 5.18 (s, 2H), 4.64-4.60 (m,1H), 4.36-4.27 (m, 2H), 3.80-3.72 (m, 3H), 3.76-3.45 (m, 4H), 2.37-2.31(m, 3H), 2.06-1.96 (m, 3H), 1.32-1.25 (m, 3H).

LCMS (m/z): 447.7 [M⁺+1]

Synthesis of(R)-1-(D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1011)

To a stirring solution of compound 3 (500 mg, 1.12 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (200 mg) at RT and stirred for 16 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (5 mL) and DCM (5 mL). Obtained filtrate wasconcentrated under reduced pressure and dried under vacuum to affordNRX-1011 (250 mg, 71%) as off white color solid.

¹H-NMR: (400 MHz, D₂O): δ 4.47-4.40 (m, 1H), 4.36-4.34 (m, 1H),4.30-4.24 (m, 1H), 3.91-3.55 (m, 4H), 3.48-3.26 (m, 3H), 2.51-2.48 (m,1H), 2.41-2.23 (m, 2H), 2.17-2.01 (m, 3H), 1.27-1.25 (m, 3H).

LCMS (ESI): m/z 313.5 [M⁺+1]

UPLC: 94.51%

Synthesis of benzyl((2S,3R)-1-((R)-2-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(4)

To a stirring solution of NRX-1011 (240 mg, 0.76 mmol) in DMF (3 mL) wasadded HATU (292 mg, 0.76 mmol), Int D (214 mg, 0.84 mmol) and DIPEA(0.26 mL, 1.53 mmol) at 0° C. under argon atmosphere. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(5 mL) and extracted with 10% MeOH/DCM (2×10 mL). Combined organiclayers were dried over anhydrous Na₂SO₄ and concentrated under reducedpressure to afford crude compound which was purified by columnchromatography by eluting with 7% MeOH/DCM to obtain compound 4 (235 mg,55%) as white solid.

¹H-NMR: (500 MHz, D₂O): δ 7.56-7.46 (m, 5H), 5.20 (s, 2H), 4.51-4.49 (m,1H), 4.37-4.27 (m, 1H), 4.12-3.96 (m, 2H), 3.78-3.73 (m, 3H), 3.64-3.55(m, 2H), 3.36-3.22 (m, 3H), 2.34-2.28 (m, 2H), 2.06-1.92 (m, 4H),1.32-1.25 (m, 6H).

LCMS (m/z): 548.5 [M⁺+1]

Synthesis of(R)-1-(L-threonyl-D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1012)

To a stirring solution of compound 4 (230 mg, 0.42 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (100 mg) at RT and stirred for 16 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Organic layer wasdried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 7% MeOH/DCM to obtain to afford NRX-1012 (65 mg, 37%) asoff brown color sticky solid.

¹H-NMR: (400 MHz, D₂O): δ 4.36-4.33 (m, 1H), 4.28-4.26 (m, 1H),3.99-3.90 (m, 2H), 3.80-3.70 (m, 4H), 3.63-3.54 (m, 2H), 3.44-3.29 (m,2H), 2.37-2.24 (m, 2H), 2.16-1.92 (m, 4H), 1.25-1.22 (m, 6H).

LCMS (ESI): m/z 414.4 [M⁺+1]

UPLC: 95.06%

G. Synthesis of NRX-1017 & 1018:

Synthesis of benzyl(R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1)

To a stirring solution of compound (SM) (15 g, 60.1 mmol) in DMF (100mL) was added EDCI (17.2 g, 90.1 mmol), HOBt (13.8 g, 90.1 mmol) andDIPEA (33.2 mL, 180.2 mmol) at 0° C. under argon atmosphere. Afterstirred for 10 minutes, Int A (8.5 g, 72.1 mmol) was added. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(20 mL) and extracted with 10% MeOH/DCM (2×20 mL). Organic layer wasdried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 3% MeOH/DCM to obtain product as thick syrup. This wasfurther triturated with TBTE to obtain compound 1 (10 g, 47%) as an offwhite solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.86-7.70 (m, 1H), 7.36-7.23 (m, 5H),7.12-7.06 (m, 2H), 5.09-5.03 (m, 2H), 4.96-4.83 (m, 1H), 4.41-4.36 (m,1H), 4.19-3.99 (m, 2H), 3.43-3.30 (m, 2H), 2.18-2.10 (m, 1H), 1.84-1.79(m, 3H), 1.01-0.96 (m, 3H).

LCMS (m/z): 350.4 [M⁺+1]

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(2)

To a stirring solution of compound 1 (10 g, 28.6 mmol) in methanol (100mL) was added 50% wet 10% Pd/C (3.5 g) at RT and stirred for 5 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas concentrated under reduced pressure. Obtained crude was trituratedwith Et₂O and dried under vacuum to afford compound 2 (4.5 g, 73%) as anoff white solid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 8.05 (d, J=8.0 Hz, 1H), 7.14 (s, 1H), 7.02(s, 1H), 4.91 (s, 1H), 4.07-4.00 (m, 2H), 3.60-3.58 (m, 1H), 2.90-2.75(m, 3H), 1.98-1.89 (m, 1H), 1.72-1.56 (m, 3H), 1.00-0.98 (m, 3H).

LCMS (ESI): m/z 216.1 [M⁺+1]

Synthesis of tert-butyl(S)-3-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of compound 2 (2 g, 9.3 mmol) in DMF (15 mL) wasadded HATU (3.53 g, 9.3 mmol), MITA (5.2 mL, 27.9 mmol) and Int B (1.99g, 9.3 mmol) at 0° C. under argon atmosphere. The reaction mixture wasbrought to RT and stirred for 16 h. After consumption of the startingmaterial (by TLC), the reaction mixture was diluted with water (5 mL)and extracted with 10% MeOH/DCM (2×30 mL). Combined organic layers weredried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 5% MeOH/DCM to obtain compound 3 (1.7 g, 44%) as an offwhite solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.83-7.76 (m, 1H), 7.10-7.02 (m, 2H),4.44-4.42 (m, 1H), 4.16-4.14 (m, 1H), 4.02-3.98 (m, 1H), 3.62-3.58 (m,2H), 3.45-3.38 (m, 2H), 3.36-3.17 (m, 4H), 1.96-1.75 (m, 6H), 1.39 (s,9H), 1.03-1.00 (m, 3H).

LCMS (m/z): 411.3 [M⁺−1]

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((S)-pyrrolidine-3-carbonyl)pyrrolidine-2-carboxamide(NRX-1017)

To a solution of compound 3 (1 g, 2.42 mmol) in DCM (10 mL) was added 4MHCl in dioxane (1.8 mL, 7.28 mmol) at 0° C. under argon atmosphere. Thereaction mixture was allowed to stir at RT for 4 h. After consumption ofthe starting material (by TLC), volatiles were evaporated under reducedpressure. Obtained crude was triturated with pentane (2×10 mL) and driedunder vacuum to afford NRX-1017 (750 mg, 88%) as an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.60-4.56 (m, 1H), 4.42-4.35 (m, 2H),3.80-3.73 (m, 2H), 3.66-3.57 (m, 2H), 3.52-3.41 (m, 3H), 2.53-2.35 (m,2H), 2.19-1.98 (m, 4H), 1.26-1.23 (m, 3H).

LCMS (ESI): m/z 313.1 [M⁺+1]

UPLC: 92.22%

Synthesis of benzyl((2S,3R)-1-((S)-3-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilyl)oxy)-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1017 (650 mg, 1.86 mmol) in DMF (10 mL)was added DIPEA (1.03 mL, 5.61 mmol) and Int C (1.03 g, 2.24 mmol) at 0°C. under argon atmosphere. The reaction mixture was brought to RT andstirred for 16 h. After consumption of the starting material (by TLC),the reaction mixture was diluted with water (5 mL) and extracted with10% MeOH/DCM (2×10 mL). Combined organic layers were dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 5%MeOH/DCM to obtain compound 5 (850 mg, 69%) as an off white solid.

¹H-NMR: (400 MHz, CD₃OD): δ 7.38-7.29 (m, 5H), 5.09 (s, 2H), 4.52-4.47(m, 1H), 4.43-4.36 (m, 2H), 4.22-4.18 (m, 1H), 4.15-4.11 (m, 1H),3.76-3.68 (m, 4H), 3.58-3.46 (m, 2H), 3.44-3.32 (m, 1H), 2.31-1.90 (m,6H), 1.20-1.16 (m, 6H), 0.87 (s, 9H), 0.07-0.04 (m, 6H).

LCMS (ESI): m/z 662.8 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((S)-3-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(6)

To a stirring solution of compound 5 (850 mg, 1.28 mmol) in THF (10 mL)was added TBAF (1M in THF) (402 mg, 1.54 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 5 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (10 mL) and extracted with 10% MeOH/DCM(2×10 mL). Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 2% MeOH/DCM to obtaincompound 6 (550 mg, 78%) as white solid.

¹H-NMR: (500 MHz, CD₃OD): δ 7.37-7.29 (m, 5H), 5.12 (s, 2H), 4.49 (s,1H), 4.49-4.33 (m, 2H), 4.20-4.18 (m, 1H), 4.04-3.91 (m, 2H), 3.82-3.72(m, 2H), 3.66-3.56 (m, 1H), 3.53-3.49 (m, 2H), 3.42-3.37 (m, 1H),2.30-2.11 (m, 4H), 2.06-2.00 (m, 2H), 1.21-1.16 (m, 6H).

LCMS (ESI): m/z 548.6 [M⁺+1]

Synthesis of(R)-1-((S)-1-(L-threonyl)pyrrolidine-3-carbonyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1018)

To a stirring solution of compound 6 (550 mg, 1.01 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (180 mg) at RT and stirred for 4 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas concentrated under reduced pressure. Obtained crude was trituratedwith pentane and dried under vacuum to afford NRX-1018 (250 mg, 60%) aswhite solid.

¹H-NMR: (400 MHz, D₂O): δ 4.58-4.54 (m, 1H), 4.42-4.37 (m, 2H),3.99-3.71 (m, 7H), 3.69-3.49 (m, 2H), 2.45-2.331 (m, 2H), 2.17-1.99 (m,4H), 1.26-1.22 (m, 6H).

LCMS (ESI): m/z 414.4 [M⁺+1]

HPLC: 99.56%

H. Synthesis of NRX-1019 & 1020:

Synthesis of benzyl(R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1)

To a stirring solution of compound (SM) (15 g, 60.1 mmol) in DMF (100mL) was added EDCI (17.2 g, 90.1 mmol), HOBt (13.8 g, 90.1 mmol) andDIPEA (33.2 mL, 180.2 mmol) at 0° C. under argon atmosphere. Afterstirred for 10 minutes, Int A (8.5 g, 72.1 mmol) was added. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was diluted with water(20 mL) and extracted with 10% MeOH/DCM (2×20 mL). Organic layer wasdried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 3% MeOH/DCM to obtain product as thick syrup. This wasfurther triturated with TBTE to obtain compound 1 (10 g, 47%) as an offwhite solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.86-7.70 (m, 1H), 7.36-7.23 (m, 5H),7.12-7.06 (m, 2H), 5.09-5.03 (m, 2H), 4.96-4.83 (m, 1H), 4.41-4.36 (m,1H), 4.19-3.99 (m, 2H), 3.43-3.30 (m, 2H), 2.18-2.10 (m, 1H), 1.84-1.79(m, 3H), 1.01-0.96 (m, 3H).

LCMS (m/z): 350.4 [M++1]

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(2)

To a stirring solution of compound 1 (10 g, 28.6 mmol) in methanol (100mL) was added 50% wet 10% Pd/C (3.5 g) at RT and stirred for 5 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas concentrated under reduced pressure. Obtained crude was trituratedwith Et₂O and dried under vacuum to afford compound 2 (4.5 g, 73%) as anoff white solid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 8.05 (d, J=8.0 Hz, 1H), 7.14 (s, 1H), 7.02(s, 1H), 4.91 (s, 1H), 4.07-4.00 (m, 2H), 3.60-3.58 (m, 1H), 2.90-2.75(m, 3H), 1.98-1.89 (m, 1H), 1.72-1.56 (m, 3H), 1.00-0.98 (m, 3H).

LCMS (ESI): m/z 216.1 [M⁺+1]

Synthesis of tert-butyl(R)-3-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of compound 2 (1 g, 4.65 mmol) in DMF (15 mL) wasadded HATU (1.76 g, 4.65 mmol), DIPEA (2.5 mL, 13.9 mmol) and Int B (1g, 4.65 mmol) at 0° C. under argon atmosphere. The reaction mixture wasbrought to RT and stirred for 16 h. After consumption of the startingmaterial (by TLC), the reaction mixture was diluted with water (5 mL)and extracted with 10% MeOH/DCM (2×20 mL). Combined organic layers weredried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 5% MeOH/DCM to obtain compound 3 (1 g, 57%) as an off whitesolid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.94-7.84 (m, 1H), 7.13-7.10 (m, 2H),4.44-4.42 (m, 1H), 4.15-4.00 (m, 2H), 3.62-3.58 (m, 2H), 3.47-3.33 (m,2H), 3.31-3.05 (m, 4H), 1.98-1.78 (m, 6H), 1.39 (s, 9H), 1.09-1.01 (m,3H).

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((R)-pyrrolidine-3-carbonyl)pyrrolidine-2-carboxamide(NRX-1019)

To a solution of compound 3 (1 g, 2.42 mmol) in DCM (10 mL) was added 4NHCl in dioxane (1.8 mL, 7.28 mmol) at 0° C. under argon atmosphere. Thereaction mixture was allowed to stir at RT for 3 h. After consumption ofthe starting material (by TLC), volatiles were evaporated under reducedpressure. Obtained crude was triturated with pentane (2×10 mL) and driedunder vacuum to afford NRX-1019 (800 mg, 95%) as an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.61-4.57 (m, 1H), 4.42-4.36 (m, 2H),3.81-3.77 (m, 2H), 3.67-3.60 (m, 1H), 3.58-3.53 (m, 2H), 3.48-3.40 (m,2H), 2.52-2.38 (m, 2H), 2.23-2.00 (m, 4H), 1.30-1.25 (m, 3H).

LCMS (ESI): m/z 313.3 [M⁺+1]

UPLC: 99.49%

Synthesis of benzyl((2S,3R)-1-((R)-3-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilyl)oxy)-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1019 (500 mg, 1.43 mmol) in DMF (5 mL) wasadded DIPEA (0.8 mL, 4.31 mmol) and Int C (799 mg, 1.72 mmol) at 0° C.under argon atmosphere. The reaction mixture was brought to RT andstirred for 5 h. After consumption of the starting material (by TLC),the reaction mixture was diluted with water (5 mL) and extracted with10% MeOH/DCM (2×10 mL). Combined organic layers were dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 2%MeOH/DCM to obtain compound 5 (700 mg, 73%) as an off white solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.93-7.83 (m, 1H), 7.34-7.25 (m, 5H), 7.05(s, 2H), 4.91 (s, 2H), 4.73-4.69 (m, 1H), 4.46-4.42 (m, 1H), 4.24-4.15(m, 2H), 4.05-4.01 (m, 2H), 3.83-3.49 (m, 4H), 2.21-1.79 (m, 6H),1.33-1.23 (m, 4H), 1.08-1.01 (m, 6H), 0.85 (s, 9H), 0.03-0.00 (m, 6H).

LCMS (ESI): m/z 662.8 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((R)-3-((R)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(6)

To a stirring solution of compound 5 (700 mg, 1.05 mmol) in THF (10 mL)was added TBAF (1M in THF) (331 mg, 1.27 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 5 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (10 mL) and extracted with 10% MeOH/DCM(2×10 mL). Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 7% MeOH/DCM to obtaincompound 6 (430 mg, 74%) as an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 7.47-7.45 (m, 5H), 5.18 (s, 2H), 4.55-4.53 (m,1H), 4.42-4.33 (m, 3H), 4.12-4.10 (m, 2H), 3.78-3.58 (m, 6H), 2.41-2.35(m, 2H), 2.18-1.95 (m, 4H), 1.30-1.22 (m, 6H).

LCMS (ESI): m/z 548.6 [M⁺+1]

Synthesis of(R)-1-((R)-1-(L-threonyl)pyrrolidine-3-carbonyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(NRX-1020)

To a stirring solution of compound 6 (230 mg, 0.42 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (70 mg) at RT and stirred for 4 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas concentrated under reduced pressure. Obtained crude was trituratedwith pentane and dried under vacuum to afford NRX-1020 (105 mg, 60%) aswhite solid.

¹H-NMR: (400 MHz, D₂O): δ 4.58-4.55 (m, 1H), 4.40-4.35 (m, 2H),4.13-4.06 (m, 1H), 3.91-3.84 (m, 1H), 3.81-3.75 (m, 4H), 3.68-3.50 (m,3H), 2.41-2.30 (m, 2H), 2.22-1.94 (m, 4H), 1.31-1.22 (m, 6H).

LCMS (ESI): m/z 414.4 [M⁺+1]

HPLC: 99.84%

Synthesis ofN-((benzyloxy)carbonyl)-O-(tert-butyldimethylsilyl)-L-threonine (Int-E)

To a stirring solution of ((benzyloxy)carbonyl)-L-threonine (SM2) (5 g,19.7 mmol) in DCM (50 mL) were added imidazole (4 g, 59.2 mmol), DMAP(241 mg, 1.97 mmol) and TBS-Cl (5.9 g, 39.5 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 18 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (10 mL) and extracted with DCM (2×20 mL).Organic layer was dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to afford crude compound which was purified by columnchromatography by eluting with 2% MeOH/DCM to obtain compound Int-E (4.1g, 57%) as an off white solid.

¹H-NMR: (500 MHz, CDCl₃): δ 7.37-7.25 (m, 5H), 5.51 (d, J=8.0 Hz, 1H),5.13 (s, 2H), 4.47 (d, J=5.0 Hz, 1H), 4.33 (d, J=8.0 Hz, 1H), 1.20 (d,J=5.0 Hz, 3H), 0.86 (s, 9H), 0.80 (s, 6H).

LCMS (m/z): 368.4 [M⁺+1]

Synthesis of 2,5-dioxopyrrolidin-1-ylN-((benzyloxy)carbonyl)-O-(tert-butyldimethylsilyl)-L-threoninate(Int-C)

To a stirring solution of compound Int-E (4.1 g, 11.1 mmol) in THF (40mL) were added DCC (2.76 g, 13.3 mmol) and NHS (1.41 g, 12.2 mmol) at 0°C. under argon atmosphere. The reaction mixture was brought to RT andstirred for 3 h. After consumption of the starting material (by TLC),the reaction mixture was diluted with water (10 mL) and extracted withEt₂O (2×20 mL). Organic layer was dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 3% MeOH/DCM to obtainInt-C(4.5 g, 86%) as semi solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.76 (d, J=9.0 Hz, 1H), 7.37-7.32 (m, 5H),5.07 (s, 2H), 4.52-4.49 (dd, J=9.0, 4.5 Hz, 1H), 4.22 (t, J=5.5 Hz, 1H),2.81 (s, 4H), 1.22 (d, J=5.5 Hz, 3H), 0.82 (s, 9H), 0.48 (s, 6H).

LCMS (m/z): 465.5 [M++1]

I. Synthesis of NRX-1021 & 1022:

Synthesis benzyl(S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1):

To a stirring solution of compound (SM) (5.0 g, 20.1 mmol) in DMF (25mL) was added DIPEA (10.5 mL, 60.3 mmol), EDCI (5.7 g, 30.15 mmol) andHOBt (4.0 g, 30.15 mmol) at 0° C. under argon atmosphere. After stirredfor 10 minutes, Int A (2.8 g, 24.1 mmol) was added. The reaction mixturewas brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was quenched with water(20 mL) and extracted with DCM (2×30 mL). Organic layer was dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 3%MeOH/DCM and then triturated with methyl tertiary-butyl ether to obtaincompound 1 (4.5 g, 64%) as an off white solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.68-7.60 (m, 1H), 7.36-7.29 (m, 5H),7.08-7.06 (m, 2H), 5.11-4.95 (m, 2H), 4.82-4.81 (m, 1H), 4.38-4.29 (m,1H), 4.16-3.97 (m, 2H), 3.44-3.31 (m, 2H), 2.19-2.10 (m, 1H), 1.88-1.79(m, 3H), 1.03-0.91 (m, 3H).

LCMS (m/z): 350.3 [M⁺+1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-2-carboxamide(2)

To a stirring solution of compound 1 (3.0 g, 8.59 mmol) in methanol (50mL) was added 50% wet 10% Pd/C (1.0 g) at RT and stirred for 4 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Obtained filtrate wasconcentrated under reduced pressure and dried under vacuum to affordcompound 2 (1.6 g, 88%) as sticky solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 8.10 (d, J=9.0 Hz, 1H), 7.20-7.16 (m, 2H),4.91 (d, J=4.5 Hz, 1H), 4.07-4.02 (m, 2H), 3.59-3.56 (m, 1H), 2.92-2.87(m, 2H), 2.78-2.73 (m, 1H), 1.97-1.91 (m, 1H), 1.70-1.57 (m, 3H),1.00-0.95 (m, 3H).

LCMS (ESI): m/z 216.0 [M⁺+1]

Synthesis of tert-butyl(R)-3-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of compound 2 (800 mg, 3.71 mmol) in DMF (5 mL)was added DIPEA (2.0 mL, 11.1 mmol), HATU (1.4 g, 3.71 mmol) and Int B(879 mg, 4.08 mmol) at 0° C. under argon atmosphere. The reactionmixture was brought to RT and stirred for 16 h. After consumption of thestarting material (by TLC), the reaction mixture was quenched with water(10 mL) and extracted with DCM (2×30 mL). Combined organic layers weredried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound 3 (900 mg, 60%) as sticky material, which wastaken to next step without any further purification.

LCMS (m/z): 413.3 [M⁺+1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((R)-pyrrolidine-3-carbonyl)pyrrolidine-2-carboxamide(NRX-1021)

To a solution of compound 3 (900 mg, 2.18 mmol) in DCM (5 mL) was added4M HCl in dioxane (0.23 mL, 6.54 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 6 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure. Obtained crude was triturated with methyltertiary-butyl ether (2×10 mL) and dried under vacuum to afford NRX-1021(540 mg, 71%) as sticky solid.

¹H-NMR: (400 MHz, D₂O): δ 4.58-4.55 (m, 1H), 4.40-4.27 (m, 2H),3.80-3.76 (m, 2H), 3.68-3.54 (m, 3H), 3.49-3.41 (m, 2H), 2.55-2.33 (m,2H), 2.22-2.03 (m, 4H), 1.30 (t, J=6.4 Hz, 3H).

LCMS (ESI): m/z 313.7[M⁺+1]

UPLC: 93.42%

Synthesis of benzyl((2S,3R)-1-((R)-3-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilypoxy)-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1021 (500 mg, 1.43 mmol) in DMF (2 mL) wasadded DIPEA (0.8 mL, 4.31 mmol) and Int D (799 mg, 1.71 mmol) at 0° C.under argon atmosphere. The reaction mixture was brought to RT andstirred for 2 h. After consumption of the starting material (by TLC),the reaction mixture was diluted with water (5 mL) and extracted with CM(2×10 mL). Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound which waspurified by column chromatography by eluting with 3% MeOH/DCM to obtaincompound 5 (600 mg, 63%) as sticky compound.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.89-7.86 (m, 1H), 7.34-7.23 (m, 5H),7.07-6.99 (m, 3H), 5.00 (s, 2H), 4.88-4.84 (m, 1H), 4.40-4.38 (m, 1H),4.27-4.15 (m, 1H), 4.02-3.99 (m, 3H), 3.82-3.80 (m, 1H), 3.67-3.54 (m,3H), 3.49-3.40 (m, 2H), 3.37-3.27 (m, 1H), 2.16-1.90 (m, 4H), 1.78 (brs, 1H), 1.23 (s, 1H), 1.09-0.97 (m, 6H), 0.85-0.81 (s, 9H), 0.02-0.02(m, 6H).

LCMS (ESI): m/z 662.8 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((R)-3-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(6)

To a stirring solution of compound 5 (600 mg, 0.91 mmol) in THF (6 mL)was added TBAF (284 mg, 1.09 mmol) at 0° C. under argon atmosphere. Thereaction mixture was brought to RT and stirred for 4 h. Afterconsumption of the starting material (by TLC), the reaction mixture wasdiluted with water (5 mL) and extracted with DCM (2×10 mL). Combinedorganic layers were dried over anhydrous Na₂SO₄ and concentrated underreduced pressure to afford crude compound which was purified by columnchromatography by eluting with 5% MeOH/DCM to obtain compound 6 (320 mg,64%) as sticky compound.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.88-7.86 (m, 1H), 7.35-7.31 (m, 5H),7.13-7.04 (m, 3H), 5.05-4.99 (m, 2H), 4.88-4.85 (m, 1H), 4.73-4.70 (m,1H), 4.39-4.37 (m, 1H), 4.17-4.15 (m, 1H), 4.04-4.02 (m, 3H), 3.82-3.79(m, 1H), 3.64-3.56 (m, 3H), 3.39-3.37 (m, 2H), 3.17-3.14 (m, 1H),2.06-1.78 (m, 4H), 1.56 (br s, 1H), 1.33-1.23 (m, 1H), 1.04-0.92 (m,6H).

LCMS (ESI): m/z 548.6 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((R)-3-((S)-2-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(NRX-1022)

To a stirring solution of compound 6 (320 mg, 0.58 mmol) in methanol (5mL) was added 50% wet 10% Pd/C (100 mg) at RT and stirred for 12 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas washed with pentane (10 mL) and Et₂O (10 mL). Obtained filtrate wasconcentrated under reduced pressure to afford crude compound which wastriturated with methyl tertiary-butyl ether (2×10 mL) and dried undervacuum to afford NRX-1022 (210 mg, 87%) as an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.58-4.52 (m, 1H), 4.35-4.26 (m, 2H),3.99-3.49 (m, 9H), 2.43-2.32 (m, 2H), 2.24-2.00 (m, 4H), 1.28-1.22 (m,6H).

LCMS (ESI): m/z 414.4 [M⁺+1]

UPLC: 95.12%

J. Synthesis of NRX-1007 & 1008:

Synthesis of tert-butyl(S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1)

To a stirring solution of(S)-1-(tert-butoxycarbonyl)pyrrolidine-3-carboxylic acid (SM) (5.0 g,25.2 mmol) in DMF (30 mL) was added DIPEA (13.1 mL, 75.7 mmol), HATU(10.5 g, 27.7 mmol) and Int A (2.9 g, 25.2 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 16 h.After consumption of the starting material (by TLC), the reactionmixture was quenched with water (20 mL) and extracted with DCM (2×30mL). Organic layer was dried over anhydrous Na₂SO₄ and concentratedunder reduced pressure to afford crude compound which was purified bycolumn chromatography by eluting with 4% MeOH/DCM to obtain compound 1(4.7 g, 59%) as white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.35 (d, J=4.0 Hz, 1H), 4.33-4.27 (m, 1H),3.62-3.37 (m, 4H), 3.31-3.24 (m, 1H), 2.31-2.23 (m, 1H), 2.13-2.04 (m,1H), 1.48 (s, 9H), 1.24 (d, J=2.4 Hz, 3H).

LCMS (m/z): 314.3 [M⁺−1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(2)

To a solution of compound 1 (1.5 g, 4.76 mmol) in DCM (25 mL) was added4M HCl in dioxane (3.6 mL, 14.2 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 4 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure and dried under vacuum to afford compound 2.HClsalt (1.2 g) as white solid.

¹H-NMR: (500 MHz, D₂O): δ 4.37-4.29 (m, 2H), 3.60-3.57 (m, 2H),3.49-3.42 (m, 3H), 2.49-2.42 (m, 1H), 2.27-2.18 (m, 1H), 1.26 (d, J=6.5Hz, 3H).

LCMS (ESI): m/z 314.5 [M⁺+1]

Synthesis of benzyl(S)-2-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of compound 2 (800 mg, 3.18 mmol) in DCM:H₂O (16mL, 1:1) was added Na₂CO₃ (844 mg, 7.97 mmol) and Int-C(1 g, 3.81 mmol)at 0° C. under argon atmosphere. The reaction mixture was stirred at RTfor 2 h. After consumption of the starting material (by TLC), thereaction mixture was extracted with DCM (2×30 mL). Organic layer wasdried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 4% MeOH/DCM to obtain compound 3 (540 mg, 38%) as an offwhite solid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.85-7.75 (m, 1H), 7.33-7.24 (m, 5H), 7.05(s, 1H), 5.10-5.00 (m, 2H), 4.92-4.89 (m, 1H), 4.84-4.82 (m, 1H),4.51-4.44 (m, 1H), 4.18-4.13 (m, 1H), 4.03-4.01 (m, 1H), 3.59-3.54 (m,2H), 3.53-3.36 (m, 3H), 3.26-3.19 (m, 1H), 3.12-3.05 (m, 1H), 2.20-2.11(m, 2H), 1.93-1.80 (m, 4H), 1.03 (d, J=6.4 Hz, 3H).

LCMS (ESI): m/z 447.6 [M⁺+1]

Synthesis of(S)-1-(L-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1007)

To a stirring solution of compound 3 (520 mg, 1.16 mmol) in methanol (15mL) was added 50% wet 10% Pd/C (200 mg) at RT and stirred for 1 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and washed withmethanol (10 mL). Obtained filtrate was concentrated under reducedpressure to afford crude compound which was triturated with Et₂O anddried under vacuum to afford NRX-1007 (310 mg, 85%) as white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.36-4.27 (m, 2H), 4.04-3.98 (m, 1H),3.89-3.51 (m, 4H), 3.45-3.29 (m, 1H), 3.15-3.11 (m, 1H), 2.95-2.88 (m,1H), 2.43-2.08 (m, 3H), 1.88-1.74 (m, 3H), 1.30-1.25 (d, J=6.4 Hz, 3H).

LCMS (ESI): m/z 313.5 [M⁺+1]

HPLC: 98.51%

Synthesis of benzyl((2S,3R)-1-((S)-2-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1007 (230 mg, 0.73 mmol) in DMF (5 mL) wasadded DIPEA (0.4 mL, 2.21 mmol), HATU (308 mg, 0.81 mmol) and Int D (223mg, 0.88 mmol) at 0° C. under argon atmosphere. The reaction mixture wasbrought to RT and stirred for 3 h. After consumption of the startingmaterial (by TLC), the reaction mixture was quenched with water (5 mL)and extracted with DCM (2×20 mL). Combined organic layers were driedover anhydrous Na₂SO₄ and concentrated under reduced pressure to affordcrude compound which was purified by column chromatography by elutingwith 6% MeOH/DCM to obtain crude compound 5 (210 mg, crude) as whitesolid, which was taken to next step without any further purification.

LCMS (m/z): 548.6 [M⁺+1]

Synthesis of(S)-1-(L-threonyl-L-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1008)

To a stirring solution of compound 5 (200 mg, 0.36 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (50 mg) at RT and stirred for 2 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and washed withmethanol (10 mL). Obtained filtrate was concentrated under reducedpressure to afford crude compound which was triturated with Et₂O (2×10mL) and dried under vacuum to afford NRX-1008 (48 mg, 31%) as whitesolid.

¹H-NMR: (400 MHz, D₂O): δ 4.80-4.70 (m, 1H), 4.40-4.28 (m, 2H),4.17-4.13 (m, 2H), 4.03-3.86 (m, 2H), 3.82-3.55 (m, 4H), 3.52-3.33 (m,1H), 2.44-2.24 (m, 2H), 2.18-2.02 (m, 3H), 1.99-1.90 (m, 1H), 1.41 (d,J=5.6 Hz, 3H), 1.28 (d, J=6.4 Hz, 3H).

LCMS (ESI): m/z 414.4 [M⁺+1]

HPLC: 94.67%

K. Synthesis of NRX-1013 & 1014:

Synthesis of tert-butyl(S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carboxylate(1)

To a stirring solution of(S)-1-(tert-butoxycarbonyl)pyrrolidine-3-carboxylic acid (SM) (5.0 g,25.12 mmol) in DMF (30 mL) was added DIPEA (13.1 mL, 75.7 mmol), HATU(10.5 g, 27.7 mmol) and Int A (2.9 g, 25.2 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 16 h.After consumption of the starting material (by TLC), the reactionmixture was quenched with water (20 mL) and extracted with DCM (2×30mL). Organic layer was dried over anhydrous Na₂SO₄ and concentratedunder reduced pressure to afford crude compound which was purified bycolumn chromatography by eluting with 4% MeOH/DCM to obtain compound 1(4.7 g, 59%) as white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.35 (d, J=4.0 Hz, 1H), 4.33-4.27 (m, 1H),3.62-3.37 (m, 4H), 3.31-3.24 (m, 1H), 2.31-2.23 (m, 1H), 2.13-2.04 (m,1H), 1.48 (s, 9H), 1.24 (d, J=2.4 Hz, 3H).

LCMS (m/z): 314.3 [M⁺−1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(2)

To a solution of compound 1 (3.5 g, 11.1 mmol) in DCM (35 mL) was added4M HCl in dioxane (0.83 mL, 3.33 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 2 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure. Crude material was triturated with Et₂O driedunder vacuum to afford compound 2.HCl salt (3.1 g) as white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.35-4.29 (m, 2H), 3.67-3.57 (m, 4H),3.44-3.41 (m, 1H), 2.51-2.38 (m, 1H), 2.28-2.16 (m, 1H), 1.26 (d, J=6.4Hz, 3H).

LCMS (ESI): m/z 215.3 [M⁺+1]

Synthesis of benzyl(R)-2-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(3)

To a stirring solution of compound 2.HCl salt (1.5 g, 5.97 mmol) inDCM:H₂O (30 mL, 1:1) was added Na₂CO₃ (1.5 g, 14.9 mmol) and Int-C(1.9g, 7.16 mmol) at 0° C. under argon atmosphere. The reaction mixture wasstirred at RT for 2 h. After consumption of the starting material (byTLC), the reaction mixture was extracted with DCM (2×30 mL). Organiclayer was dried over anhydrous Na₂SO₄ and concentrated under reducedpressure to afford crude compound which was purified by columnchromatography by eluting with 5% MeOH/DCM to obtain compound 3 (1.1 g,42%) as an off white solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.79-7.76 (m, 1H), 7.38-7.26 (m, 5H), 7.06(s, 1H), 5.09-5.00 (m, 2H), 4.94-4.91 (m, 1H), 4.84-4.82 (m, 1H),4.45-4.41 (m, 1H), 4.15-4.13 (m, 1H), 4.04-4.01 (m, 1H), 3.69-3.66 (m,1H), 3.49-3.41 (m, 2H), 3.31-3.21 (m, 2H), 3.07-2.97 (m, 2H), 2.19-2.12(m, 2H), 1.89-1.80 (m, 4H), 1.04-1.01 (d, 3H).

LCMS (ESI): m/z 447.5 [M⁺+1]

Synthesis of(S)-1-(D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1013)

To a stirring solution of compound 3 (1.1 g, 2.46 mmol) in methanol (25mL) was added 50% wet 10% Pd/C (300 mg) at RT and stirred for 1 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and washed withmethanol (10 mL). Obtained filtrate was concentrated under reducedpressure. Crude material was triturated with Et₂O and dried under vacuumto afford crude compound which was triturated with Et₂O and dried undervacuum to afford NRX-1013 (620 mg, 80%) as white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.37-4.29 (m, 2H), 3.93-3.88 (m, 1H),3.76-3.60 (m, 3H), 3.42-3.30 (m, 2H), 3.11-3.06 (m, 1H), 2.86-2.81 (m,1H), 2.40-2.12 (m, 3H), 1.85-1.69 (m, 3H), 1.25 (d, J=6.4 Hz, 3H).

LCMS (ESI): m/z 313.3 [M⁺+1]

HPLC: 99.56%

Synthesis of benzyl((2S,3R)-1-((R)-2-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilyl)oxy)-1-oxobutan-2-yl)carbamate(5)

To a stirring solution of NRX-1013 (300 mg, 0.96 mmol) in DMF (5 mL) wasadded DIP EA (0.4 mL, 1.93 mmol) and Int D (535 mg, 1.15 mmol) at 0° C.under argon atmosphere. The reaction mixture was brought to RT andstirred for 2 h. After consumption of the starting material (by TLC),the reaction mixture was quenched with water (5 mL) and extracted withDCM (2×20 mL). Combined organic layers were dried over anhydrous Na₂SO₄and concentrated under reduced pressure to afford crude compound 5 (710mg, crude), which was taken to next step without any furtherpurification.

LCMS (m/z): 662.3 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((R)-2-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(6)

To a stirring solution of crude compound 5 (710 mg, 1.07 mmol) in THF(10 mL) was added TBAF (336 mg, 1.29 mmol) at 0° C. under argonatmosphere. The reaction mixture was brought to RT and stirred for 4 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (5 mL) and extracted with DCM (2×10 mL).Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford crude compound 6 (230 mg,crude) as sticky compound, which was taken to next step without anyfurther purification.

LCMS (ESI): m/z 548.6 [M⁺+1]

Synthesis of(S)-1-(L-threonyl-D-prolyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1014)

To a stirring solution of compound 6 (230 mg, 0.42 mmol) in methanol (15mL) was added 50% wet 10% Pd/C (100 mg) at RT and stirred for 2 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and washed withmethanol (10 mL). Obtained filtrate was concentrated under reducedpressure to afford NRX-1014 (53 mg, 30%) as an off white sticky solid.

¹H-NMR: (400 MHz, D₂O): δ 4.80-4.70 (m, 2H), 4.41-4.30 (m, 2H),4.03-4.00 (m, 1H), 3.89-3.71 (m, 5H), 3.63-3.58 (m, 1H), 3.36-3.33 (m,1H), 2.45-2.32 (m, 2H), 2.15-1.94 (m, 4H), 1.28-1.25 (m, 6H).

LCMS (ESI): m/z 414.4 [M⁺+1]

HPLC: 95.75%

L. Synthesis of NRX-1027 & 1028:

Synthesis of tert-butyl(R)-3-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(2)

To a stirring solution of Int-A (740 mg, 2.51 mmol) in DMF (3 mL) wasadded DIPEA (1.3 mL, 7.52 mmol) followed by compound 1 (596 mg, 2.51mmol) at 0° C. under argon atmosphere. The reaction mixture was broughtto RT and stirred for 4 h. After consumption of the starting material(by TLC), the reaction mixture was diluted with water (10 mL) andextracted with DCM (2×50 mL). Combined organic layers were dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 5%MeOH/DCM to obtain compound 2 (476 mg, 48%) as a white solid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.76 (d, J=9.2 Hz, 1H), 7.20 (s, 1H), 7.04(s, 1H), 4.17-4.12 (m, 1H), 4.02-3.96 (m, 1H), 3.75-3.42 (m, 6H),3.24-3.08 (m, 5H), 2.09-2.00 (m, 2H), 1.96-1.85 (m, 2H), 1.39 (s, 9H),1.03-1.00 (d, J=7.2 Hz, 3H).

LCMS (m/z): 313.3 [M⁺+1-Boc]

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((R)-pyrrolidine-3-carbonyl)pyrrolidine-3-carboxamide(NRX-1027)

To a stirring solution of compound 2 (470 mg, 1.44 mmol) in DCM (5 mL)was added 4N HCl in dioxane (1.4 mL, 5.70 mmol) at 0° C. under nitrogenatmosphere. The reaction mixture was allowed to stir at RT for 2 h.After consumption of the starting material (by TLC), volatiles wereevaporated under reduced pressure. Obtained crude was washed withpentane (2×10 mL) and dried under vacuum to afford NRX-1027.HCl salt(402 mg, crude) as a white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.35-4.33 (m, 1H), 4.29-4.24 (m, 1H),3.92-3.30 (m, 10H), 2.48-2.10 (m, 4H), 1.27-1.24 (m, 3H).

LCMS (ESI): m/z 313.5 [M⁺+1]

HPLC: 98.64%

Synthesis of benzyl((2S,3R)-1-((R)-3-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilypoxy)-1-oxobutan-2-yl)carbamate(3)

To a stirring solution of NRX-1027.HCl salt (150 mg, 0.43 mmol) in DMF(3 mL) were added DIPEA (0.22 mL, 1.29 mmol) and Int-B (239 mg, 0.52mmol) and at 0° C. under nitrogen atmosphere. The reaction mixture wasbrought to RT and stirred for 16 h. After consumption of the startingmaterial (by TLC), the reaction mixture was diluted with water (10 mL)and extracted with DCM (2×20 mL). Combined organic layers were driedover anhydrous Na₂SO₄ and concentrated under reduced pressure to affordcrude compound which was purified by column chromatography by elutingwith 8% MeOH/DCM to obtain compound 3 (205 mg, 72%) as a brown solid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.81-7.76 (m, 1H), 7.35-7.29 (m, 5H), 7.20(s, 1H), 7.05-6.99 (m, 2H), 5.00 (s, 2H), 4.83-4.81 (m, 1H), 4.26-4.22(m, 1H), 4.16-4.12 (m, 1H), 4.01-3.99 (m, 2H), 3.71-3.47 (m, 7H),3.30-3.10 (m, 3H), 2.07-1.84 (m, 4H), 1.27-1.22 (m, 3H), 1.03-1.00 (m,3H), 0.81 (s, 9H), 0.03-0.00 (m, 6H).

LCMS (m/z): 662.8 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((R)-3-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(4)

To a stirring solution of compound 3 (470 mg, 0.72 mmol) in THF (5 mL)was added TBAF (1M in THF) (0.86 mL, 0.86 mmol) at 0° C. under nitrogenatmosphere. The reaction mixture was brought to RT and stirred for 6 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (5 mL) and extracted with DCM (2×10 mL).Combined organic layers were dried over anhydrous Na₂SO₄ andconcentrated under reduced pressure to afford compound 4 (395 mg, crude)as a brown compound, which was taken to next step without any furtherpurification.

LCMS (ESI): m/z 548.5 [M⁺+1]

Synthesis of(R)-1-((R)-1-(L-threonyl)pyrrolidine-3-carbonyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1028)

To a stirring solution of crude compound 5 (390 mg, 0.71 mmol) inmethanol (5 mL) was added 50% wet 10% Pd/C (150 mg) at RT and stirredfor 4 h under H₂ atmosphere. After consumption of the starting material(by TLC), the reaction mixture was filtered through a pad of celite andthe filtrate was concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 15%MeOH/DCM+2 mL aq.NH₃ to obtain to afford NRX-1028 (35 mg, 12%) as awhite solid.

¹H-NMR: (400 MHz, D₂O): δ 4.37-4.35 (m, 1H), 4.29-4.25 (m, 1H),3.98-3.85 (m, 2H), 3.84-3.32 (m, 10H), 2.38-2.05 (m, 4H), 1.27-1.22 (m,6H).

LCMS (ESI): m/z 414.4 [M⁺+1]

UPLC: 94.07%

M. Synthesis of NRX-1025 & 1026:

Synthesis of tert-butyl(S)-3-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(2)

To a stirring solution of Int-A (1.6 g, 5.12 mmol) in DMF (6 mL) wasadded DIPEA (2.6 mL, 15.4 mmol) followed by compound 1 (1.3 g, 5.12mmol) at 0° C. under argon atmosphere. The reaction mixture was broughtto RT and stirred for 16 h. After consumption of the starting material(by TLC), the reaction mixture was diluted with water (10 mL) andextracted with DCM (2×50 mL) and 10% MeOH/DCM. Combined organic layerswere dried over anhydrous Na₂SO₄ and concentrated under reduced pressureto afford crude compound which was purified by column chromatography byeluting with 8% MeOH/DCM to obtain compound 2 (720 mg, 34%) as a brownsolid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.77 (d, J=9.0 Hz, 1H), 7.20 (s, 1H), 7.04(s, 1H), 4.15-4.13 (m, 1H), 4.01-3.98 (m, 1H), 3.65-3.41 (m, 4H),3.35-3.32 (m, 1H), 3.30-3.10 (m, 6H), 2.09-2.01 (m, 2H), 1.96-1.88 (m,2H), 1.39 (s, 9H), 1.25 (d, J=8.5 Hz, 3H).

LCMS (m/z): 313.3 [M⁺+1-Boc]

Synthesis of(R)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((S)-pyrrolidine-3-carbonyl)pyrrolidine-3-carboxamide(NRX-1025)

To a stirring solution of compound 2 (600 mg, 1.45 mmol) in DCM (5 mL)was added 4M HCl in dioxane (1.8 mL, 7.28 mmol) at 0° C. under nitrogenatmosphere. The reaction mixture was allowed to stir at RT for 4 h.After consumption of the starting material (by TLC), volatiles wereevaporated under reduced pressure. Obtained crude was washed withpentane (2×10 mL) and dried under vacuum to afford NRX-1025.HCl salt(350 mg, 69%) as a white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.34-4.30 (m, 1H), 4.29-4.23 (m, 1H),3.90-3.30 (m, 10H), 2.49-2.10 (m, 4H), 1.47-1.24 (m, 3H).

LCMS (ESI): m/z 313.3 [M⁺+1]

HPLC: 91.72%

Synthesis of benzyl((2S,3R)-1-((S)-3-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilypoxy)-1-oxobutan-2-yl)carbamate(3)

To a stirring solution of NRX-1025.HCl salt (400 mg, 1.14 mmol) in DMF(6 mL) were added DIPEA (0.59 mL, 3.44 mmol) and Int-B (639 mg, 1.37mmol) at 0° C. under nitrogen atmosphere. The reaction mixture wasbrought to RT and stirred for 16 h. After consumption of the startingmaterial (by TLC), the reaction mixture was diluted with water (10 mL)and extracted with 10% MeOH/DCM (2×20 mL). Combined organic layers weredried over anhydrous Na₂SO₄ and concentrated under reduced pressure toafford crude compound which was purified by column chromatography byeluting with 7% MeOH/DCM to obtain compound 3 (390 mg, 51%) as brownsolid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.80-7.74 (m, 1H), 7.36-7.29 (m, 5H), 7.18(s, 1H), 7.10-7.04 (m, 2H), 5.00 (s, 2H), 4.84-4.82 (m, 1H), 4.24-4.21(m, 1H), 4.18-4.16 (m, 1H), 4.03-3.97 (m, 2H), 3.88-3.77 (m, 1H),3.42-3.23 (m, 6H), 3.19-3.08 (m, 3H), 2.07-2.04 (m, 2H), 1.96-1.82 (m,2H), 1.08-1.01 (m, 6H), 0.79 (s, 9H), 0.01-0.02 (d, 6H).

LCMS (m/z): 662.8 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((S)-3-((R)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(4)

To a stirring solution of compound 3 (385 mg, 0.58 mmol) in THF (5 mL)was added TBAF (1M in THF) (0.69 mL, 0.69 mmol) at 0° C. under nitrogenatmosphere. The reaction mixture was brought to RT and stirred for 6 h.After consumption of the starting material (by TLC), the reactionmixture was diluted with water (5 mL) and extracted with DCM (2×10 mL)and 10% MeOH/DCM (2×10 mL). Combined organic layers were dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting with 7%MeOH/DCM to obtain compound 4 (270 mg, 85%) as white color compound.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.81-7.76 (m, 1H), 7.38-7.29 (m, 5H), 7.20(s, 1H), 7.11-7.05 (m, 2H), 5.06-4.99 (m, 2H), 4.84-4.82 (m, 1H),4.74-4.70 (m, 1H), 4.22-4.12 (m, 2H), 4.01-3.97 (m, 1H), 3.88-3.77 (m,2H), 3.64-3.38 (m, 6H), 3.31-3.09 (m, 3H), 2.07-1.82 (m, 4H), 1.05-1.00(m, 6H).

LCMS (ESI): m/z 548.5 [M⁺+1]

Synthesis of(R)-1-((S)-1-(L-threonyl)pyrrolidine-3-carbonyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1026)

To a stirring solution of compound 4 (260 mg, 0.47 mmol) in methanol (5mL) was added 50% wet 10% Pd/C (100 mg) at RT and stirred for 4 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and the filtratewas concentrated under reduced pressure to afford crude compound whichwas purified by column chromatography by eluting with 15% MeOH/DCM+2 mLaq.NH₃ to obtain to afford NRX-1026 (65 mg, 33%) as white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.36-4.34 (m, 1H), 4.31-4.25 (m, 1H),3.99-3.87 (m, 2H), 3.84-3.31 (m, 10H), 2.38-2.00 (m, 4H), 1.27-1.22 (m,6H).

LCMS (ESI): m/z 414.5 [M⁺+1]

UPLC: 99.84%

N. Synthesis of NRX-1029 & 1030:

Synthesis of tert-butyl(R)-3-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(2)

To a stirring solution of compound 1 (1.3 g, 5.17 mmol) in DMF (5 mL)was added DIPEA (2.8 mL, 15.5 mmol) and Int-A (1.9 g, 6.21 mmol) at 0°C. under argon atmosphere. The reaction mixture was brought to RT andstirred for 4 h. After consumption of the starting material (by TLC),the reaction mixture was quenched with water (5 mL) and extracted withDCM (2×20 mL). Combined organic layers were dried over anhydrous Na₂SO₄and concentrated under reduced pressure to afford crude compound whichwas purified by column chromatography by eluting 5% MeOH/DCM to obtaincompound 2 (750 mg, 35%) as off white solid.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.76 (d, J=8.8 Hz, 1H), 7.20 (s, 1H), 7.04(s, 1H), 4.82 (t, J=5.6 Hz, 1H), 4.14-4.10 (m, 1H), 4.04-3.98 (m, 1H),3.70-3.33 (m, 6H), 3.27-3.11 (m, 4H), 2.18-1.84 (m, 4H), 1.39 (s, 9H),1.01 (d, J=6.4 Hz, 3H).

LCMS (m/z): 411.3 [M⁺−1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((R)-pyrrolidine-3-carbonyl)pyrrolidine-3-carboxamide(NRX-1029)

To a solution of compound 2 (400 mg, 0.97 mmol) in DCM (2 mL) was added4M HCl in dioxane (0.7 mL, 2.91 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 4 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure. Crude material was triturated with Et₂O driedunder vacuum to afford NRX-1029.HCl salt (220 mg) as off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.39-4.31 (m, 2H), 3.89-3.62 (m, 4H),3.45-3.24 (m, 3H), 3.21-3.06 (m, 3H), 2.43-2.11 (m, 3H), 2.02-1.93 (m,1H), 1.28 (d, J=6.4 Hz, 3H).

LCMS (ESI): m/z 313.5 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((R)-3-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilypoxy)-1-oxobutan-2-yl)carbamate(3)

To a stirring solution of NRX-1029.HCl salt (220 mg, 0.65 mmol) in DMF(5 mL) was added DIPEA (0.2 mL, 1.26 mmol) and Int-B (351 mg, 0.75 mmol)at 0° C. under argon atmosphere. The reaction mixture was brought to RTand stirred for 16 h. After consumption of the starting material (byTLC), the reaction mixture was quenched with water (5 mL) and extractedwith DCM (2×20 mL). Combined organic layers were dried over anhydrousNa₂SO₄ and concentrated under reduced pressure to afford crude compoundwhich was purified by column chromatography by eluting 5% MeOH/DCM toobtain compound 3 (200 mg, 47%) as sticky solid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.82-7.76 (m, 1H), 7.37-7.30 (m, 5H), 7.21(s, 1H), 7.05-6.95 (m, 2H), 5.00 (s, 2H), 4.83 (m, 1H), 4.26-4.22 (m,1H), 4.14-4.12 (m, 1H), 4.04-4.01 (m, 2H), 3.60-3.34 (m, 6H), 3.31-3.21(m, 2H), 3.17-3.12 (m, 2H), 2.12-1.86 (m, 4H), 1.09-1.02 (m, 6H), 0.81(s, 9H), 0.02 (s, 3H), −0.00 (s, 3H).

LCMS (m/z): 411.3 [M⁺−1]

Synthesis of benzyl((2S,3R)-1-((R)-3-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(4)

To a stirring solution of compound 3 (200 mg, 0.31 mmol) in THF (2 mL)was added TBAF (94 mg, 0.37 mmol) at 0° C. under argon atmosphere. Thereaction mixture was brought to RT and stirred for 4 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedto obtain crude compound which was purified by column chromatography byeluting 5% MeOH/DCM to obtain crude compound 4 (170 mg) as an off whitesolid.

¹H-NMR: (500 MHz, DMSO-d₆): δ 7.81-7.79 (m, 1H), 7.35-7.31 (m, 5H), 7.21(s, 1H), 7.13-7.05 (m, 2H), 5.05-4.98 (m, 2H), 4.83-4.81 (m, 1H),4.73-4.71 (m, 1H), 4.22-4.13 (m, 2H), 4.04-4.01 (m, 1H), 3.85-3.83 (m,1H), 3.74-3.48 (m, 6H), 3.31-3.25 (m, 2H), 3.16-3.11 (m, 2H), 2.12-2.01(m, 3H), 1.90-1.83 (m, 1H), 1.06-1.04 (m, 6H).

LCMS (ESI): m/z 662.3 [M⁺+1]

Synthesis of(S)-1-((R)-1-(L-threonyl)pyrrolidine-3-carbonyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1030)

To a stirring solution of crude compound 4 (170 mg, 0.31 mmol) inmethanol (5 mL) was added 50% wet 10% Pd/C (75 mg) at RT and stirred for3 h under H₂ atmosphere. After consumption of the starting material (byTLC), the reaction mixture was filtered through a pad of celite andwashed with methanol (10 mL). Obtained filtrate was concentrated underreduced pressure to afford NRX-1030 (52 mg, 45%) as a sticky compound.

¹H-NMR: (400 MHz, D₂O): δ 4.39-4.29 (m, 2H), 4.04-4.01 (m, 1H),3.90-3.33 (m, 11H), 2.42-2.08 (m, 4H), 1.29-1.26 (m, 6H).

LCMS (ESI): m/z 414.4 [M⁺+1]

LCMS: 99.83%

O. Synthesis of NRX-1023 & 1024:

Synthesis of tert-butyl(S)-3-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidine-1-carboxylate(2)

To a stirring solution of compound 1 (595 mg, 2.37 mmol) in DMF (4 mL)was added DIPEA (1.3 mL, 7.11 mmol) and Int-A (740 mg, 2.37 mmol) at 0°C. under argon atmosphere. The reaction mixture was brought to RT andstirred for 4 h. After consumption of the starting material (by TLC),the reaction mixture was quenched with water (5 mL) and extracted withDCM (2×20 mL). Combined organic layers were dried over anhydrous Na₂SO₄and concentrated under reduced pressure to afford crude compound whichwas purified by column chromatography by eluting 2% MeOH/DCM to obtaincompound 2 (350 mg, 35%) as thick syrup.

¹H-NMR: (400 MHz, DMSO-d₆): δ 7.78 (d, J=8.8 Hz, 1H), 7.21 (s, 2H), 4.83(t, J=5.6 Hz, 1H), 4.15-4.10 (m, 1H), 4.02 (br s, 1H), 3.72-3.50 (m,2H), 3.49-3.40 (m, 2H), 3.37-3.33 (m, 2H), 3.28-3.07 (m, 4H), 2.17-1.85(m, 4H), 1.39 (s, 9H), 1.02 (d, J=6.4 Hz, 3H).

LCMS (m/z): 411.3 [M⁺−1]

Synthesis of(S)—N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)-1-((S)-pyrrolidine-3-carbonyl)pyrrolidine-3-carboxamide(NRX-1023)

To a solution of compound 2 (350 mg, 0.84 mmol) in DCM (2 mL) was added4M HCl in dioxane (0.6 mL, 2.54 mmol) at 0° C. under argon atmosphere.The reaction mixture was allowed to stir at RT for 2 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedunder reduced pressure. Crude material was triturated with Et₂O driedunder vacuum to afford NRX-1023.HCl salt (330 mg) as off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.37-4.28 (m, 2H), 3.90-3.18 (m, 10H),2.41-2.01 (m, 4H), 1.25 (d, J=6.4 Hz, 3H).

LCMS (ESI): m/z 313.5 [M⁺+1]

Synthesis of benzyl((2S,3R)-1-((S)-3-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-((tert-butyldimethylsilypoxy)-1-oxobutan-2-yl)carbamate(3)

To a stirring solution of NRX-1023.HCl salt (700 mg, 2.01 mmol) in DMF(10 mL) was added DIPEA (0.7 mL, 4.02 mmol) and Int-B (1.1 g, 2.41 mmol)at 0° C. under argon atmosphere. The reaction mixture was brought to RTand stirred for 16 h. After consumption of the starting material (byTLC), the reaction mixture was quenched with water (5 mL) and extractedwith 10% MeOH/DCM (2×20 mL). Combined organic layers were dried overanhydrous Na₂SO₄ and concentrated under reduced pressure to afford crudecompound which was purified by column chromatography by eluting 2%MeOH/DCM to obtain compound 3 (700 mg, 53%) as an off white solid.

LCMS (m/z): 662.3 [M⁺−1]

Synthesis of benzyl((2S,3R)-1-((S)-3-((S)-3-(((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)carbamoyl)pyrrolidine-1-carbonyl)pyrrolidin-1-yl)-3-hydroxy-1-oxobutan-2-yl)carbamate(4)

To a stirring solution of compound 3 (500 mg, 1.08 mmol) in THF (5 mL)was added TBAF (501 mg, 1.91 mmol) at 0° C. under argon atmosphere. Thereaction mixture was brought to RT and stirred for 4 h. Afterconsumption of the starting material (by TLC), volatiles were evaporatedto obtain crude compound which was purified by column chromatography byeluting 6% MeOH/DCM to obtain compound 4 (300 mg, 51%) as an off whitesolid.

LCMS (ESI): m/z 548.6 [M⁺+1]

Synthesis of(S)-1-((S)-1-(L-threonyl)pyrrolidine-3-carbonyl)-N-((2S,3R)-1-amino-3-hydroxy-1-oxobutan-2-yl)pyrrolidine-3-carboxamide(NRX-1024)

To a stirring solution of compound 4 (300 mg, 0.54 mmol) in methanol (10mL) was added 50% wet 10% Pd/C (100 mg) at RT and stirred for 16 h underH₂ atmosphere. After consumption of the starting material (by TLC), thereaction mixture was filtered through a pad of celite and washed withmethanol (10 mL). Obtained filtrate was concentrated under reducedpressure to afford NRX-1024 (90 mg, 39%) as an off white solid.

¹H-NMR: (400 MHz, D₂O): δ 4.36-4.27 (m, 2H), 4.02-3.91 (m, 1H),3.91-3.29 (m, 11H), 2.40-2.02 (m, 4H), 1.24-1.22 (m, 6H).

LCMS (ESI): m/z 414.5 [M⁺+1]

LCMS: 93.08%

Example 5—Biological Data

I. In Vitro [³H]MK-801 Potentiation Assay: Overview

Rat Cortical Membrane Preparation

Crude synaptic membranes were prepared using rat telencephalon (frontalcortex and hippocampus tissue) from male Sprague-Dawley rats andextensively washed using procedures modified from the Moskal et al. 2001Review; The use of antibody engineering to create novel drugs thattarget N-methyl-D-aspartate receptors, Current Drug Targets,2(3):331-45. Briefly, tissue that had been stored at −80° C. washomogenized in ice cold 10 mM Tris (pH7.4 at 4° C.) using a BrinkmanPolytron and then pelleted by centrifugation at 51,500 g for 20 min. Theresulting supernatant was discarded and the membranes were homogenizedand washed an additional 3×. Pellets were then resuspended in 5 mMEDTA/15 mM Tris (pH7.4) and incubated for 1 hr at 37° C. The membranesuspensions were then pelleted by centrifugation at 51,500 g for 20 minand stored at −80° C. overnight. The pellets were resuspended in 10 mMTris HCl (pH7.4 at 4° C.) and homogenized and washed an additional 7times and frozen at 80° C. until assay.

Assay

Functional glycine site agonist effects were measured using an a[³H]MK-801 potentiation assay (see Urwyler S, Floersheim P, Roy B L,Koller M. J Med Chem. (2009) 52(16):5093-107). Briefly, 300 μg ofmembrane extract protein were preincubated for 15 minutes at 25° C. inthe presence of a saturating concentration of glutamate (50 μM) andvarying concentrations of GLYX-13. Following the addition of 0.3 mCi of[³H]MK-801 (Amersham, 22.5 Ci/mmol), reactions were incubated for anadditional 15 minutes (non-equilibrium conditions). Bound and free[³H]MK-801 were separated via rapid filtration using a Brandelapparatus. Zero levels were determined in the absence of any glycineligand in the presence of 30 μM dichlorokyneurenic acid. The % maximal[³H]MK-801 binding was calculated relative to stimulation measured inthe presence of 1 mM glycine and 50 μM glutamate. Binding curves werefitted using GraphPad software.

For compounds with relatively low activity (e.g., GLYX-13), theidentification and elimination of background glycine levels can have asignificant effect on the interpretation of this assay. The origin ofaberrantly high background glycine, or bioactive plastic leachates thatact like glycine, can stemrom either the water itself, the LC/MS gradewater filter used, or a result of time-dependent leaching fromplasticware (including storage tubes, beakers, pipette tips). As such,determination of background glycine levels that may be present in theassay solutions is performed prior to any preclinical assay. Absolutebackground percentages are calculated.

To minimize the effect of high background, a full glycine dose responseis run in the presence and absence of 5.7 dichlorokyneurenic acid todetermine the absolute zero background glycine levels. The measuredbackground in this assay is preferably not greater than 5-10%.

II. In Vitro [³H]MK-801 Potentiation Assay: Preparation of Rat CorticalMembranes

Solutions Utilized:

-   2 L of 10 mM Tris HCl (pH7.4 at 4° C.)-   1 L 5 mM EDTA/15 mM Tris (pH7.4)-   1 L 10 mM Tris Acetate (pH7.4 at 4° C.)

Reagents Utilized:

-   Trizma Base-   3 L Reagent grade H₂O-   EDTA-   2N HCl-   Glacial acetic acid

Materials Utilized:

-   Rat whole brains (8 max)-   Polytron homogenizer-   JA 20.1 rotor centrifuge tubes-   50 ml conical tubes-   20 ml pipette tips-   10 ml pipette tips-   5 ml pipette tips    Experimental Design    One Day Prior:

Prepare 1 L of 10 mM Tris HCl (pH7.4 at 4° C.)

-   -   1.2112 g Trizma Base (FW 121.14) to 1 L milliQ H₂O    -   Add 2N HCl until pH is 7.4 at 4° C. (˜4 ml HCl needed)        Store at 4° C. overnight and use cold

Make 1 L of 15 mM Tris HCl/5 mM EDTA (pH7.4 at room temp)

-   -   1.8168 g Trizma Base (FW 121.14)    -   1.4612 g EDTA, anhydrous (MW 292.24) to 1 L MilliQ H₂O    -   Add 2N HCl until pH is 7.4 at 4° C.        Store at room temperature overnight        Day 1:

Cool centrifuge and JA 20.1 rotor to 4° C. before starting the membraneisolation.

Turn on the 37° C. water bath and put 5 mM EDTA/15 mM Tris (pH7.4) at37° C.

Cool Polytron homogenizer by putting in 50 ml conical tube with reagentgrade H₂O on ice. Place JA 20.1 centrifuge tubes on ice at 4° C. to coolbefore adding rat cortical dissections (2/brain being homogenized with amaximum of 16 tubes). In addition, cool to 4° C. the 50 ml tubes thatwill be used to homogenize rat brains (1/brain being homogenized for amaximum of 8 tubes) and the 10 mM Tris HCl (pH7.4 at 4° C.) to be usedin the isolation.

Remove the previously dissected and frozen rat telencephalon (frontalcortex and hippocampus tissue from male Sprague-Dawley rats; 8 max) fromthe −80° C. freezer and place on ice. Add 24 ml of 10 mM Tris HCl (pH7.4at 4° C.) to each of these 50 ml conical tubes and keep them on ice.Homogenize on setting 3.5 of the Polytron homogenizer until the tissueis completely suspended. Add 12 ml to each of two JA 20.1 centrifugetubes, also on ice. Centrifuge at 51,500×g for 30 min at 4° C. Clean thePolytron homogenizer by running the homogenizer in MilliQ water andwiping clean with a Kimwipe. Keep the homogenizer cold betweenhomogenizations by putting it in 50 ml conical tube with reagent gradeH₂O on ice.

After the 30 min centrifugation step pour off the supernatant leavingthe cell pellet. Add 3 ml of 10 mM Tris HCl (pH7.4 at 4° C.) andresuspend the membranes by homogenization for 30 seconds on setting 3.5of the Polytron homogenizer, or until completely resuspended. Once themembranes are resuspended add an additional 9 ml of 10 mM Tris HCl (7.4at 4 C) for a total volume of 12 ml. Again, centrifuge at 51,500×g for30 min at 4° C. Clean the Polytron homogenizer as before and repeat 3times for a total of 4 wash steps.

After the final wash step, to the cell pellet, add 3 ml of 5 mM EDTA/15mM Tris (pH7.4) previously incubated at 37° C. and resuspend byhomogenization on setting 3.5 of the Polytron homogenizer. Add anadditional 9 ml of 5 mM EDTA/15 mM Tris (pH7.4 at 37° C.) for a totalvolume of 12 ml. Cover the JA 20.1 centrifuge tubes with parafilm andincubate the samples in a 37° C. water bath for 1 hour (Note: be carefulto ensure that the water level does not cover the top of the centrifugetubes). Remove the parafilm from the centrifuge tubes and thencentrifuge them at 51,500×g for 30 min at 4° C. Pour off thesupernatant. Cover the JA 20.1 centrifuge tubes with parafilm and quickfreeze the rat cortical pellet by immersing the centrifuge tubecontaining the pellet in liquid nitrogen until completely frozen. Storethe membrane extract at −80° C.

Prepare 1 L of 10 mM Tris HCl (pH7.4 at 4° C.)

-   -   1.2112 g Trizma Base (FW 121.14) to 1 L reagent grade H₂O    -   Add 2N HCl until pH is 7.4 at 4° C. (˜4 ml HCl needed)        Store at 4° C. overnight for use on Day 2.        Day 2:

Prepare 1 L of 10 mM Tris Acetate (pH7.4 at Room Temperature)

-   -   1.2112 g Trizma Base (FW 121.14) to 1 L reagent grade H₂O    -   Add glacial acetic acid until pH is 7.4 at room temperature

Cool centrifuge to 4° C. to allow it to reach temperature beforestarting the membrane preparation and put the JA 20.1 rotor in thecentrifuge. Cool Polytron homogenizer by putting in 50 ml conical tubewith reagent grade H₂O on ice. Put the 10 mM Tris HCl (pH 0.4 at 4° C.)stored at 4° on ice to keep cool.

Remove the frozen membrane extracts made on day one from the −80° C.freezer and put on ice. Add 3 ml of 10 mM Tris HCl (pH7.4 at 4° C.) andhomogenize on setting 3.5 of the Polytron homogenizer until the pelletis completely in suspension. Once the membranes are resuspended add anadditional 9 ml of 10 mM Tris HCl (pH7.4 at 4 C) for a total volume of12 ml. Centrifuge at 51,500×g for 30 min at 4° C. Clean the Polytronhomogenizer by running the homogenizer in MilliQ water and wiping cleanwith a Kimwipe. Keep the homogenizer cold by putting it in 50 ml conicaltube with reagent grade H₂O on ice. Repeat 6 times for a total of 7 washsteps.

After the seventh wash step in Tris HCl, add 3 ml of 10 mM Tris Acetateto each sample and homogenize until completely resuspended. Pool thesamples in a 50 ml conical tube and quantify the protein levels usingthe BCA assay.

Once protein levels are quantified, aliquot 5 mg of rat corticalmembrane extracts into 50 ml conical tubes and label them with thevolume, protein concentration, date, and your name. Store these aliquotsat −80° C. until use in the Brandel Assay.

III. in vitro [³H]MK-801 Potentiation Assay: Brandel Rapid Filtration

Solutions Utilized:

-   10 mM Tris Acetate (pH7.4 at room temp)-   500 mM Glycine-   10 mM Glutamate-   30 mM DCK-   100 mM 7CK

Reagents Utilized:

-   LC/MS grade MilliQ water-   Trizma Base-   glacial acetic acid

Materials Utilized:

-   Previously frozen, aliquoted, and tested rat cortical membrane preps-   50 ml conical tubes-   10 ml pipette tips    -   5 ml pipette tips    -   1.5 ml tubes

Stock Solutions (these can be made in advance):

-   -   500 mM Glycine in 10 mM TA

Total Volume: 10 ml Add glycine 0.375 g 10 mM TA to 10 ml Store at 4° C.

-   -   10 mM Glutamate in 10 mM TA

Total Volume: 10 ml Add L-glutamate 0.0147 g 10 mM TA to 10 ml pH to 7.4using 10N NaOH Store at 4° C.

-   -   30 mM 5,7 dichlorokyneurenic acid (DCK) in DMSO

Total Volume: 1 ml Add DCK 0.0083 g Dimethyl sulfoxide (DMSO) 1.0 mlStore at 4° C.Experimental DesignPrepare 10 mM Tris Acetate (pH7.4 at 25° C.)

Add 1.2114 g Trizma Base/L of MilliQ LC/MS grade H₂O and mix using astir-rod. After mixing, pH the solution to pH7.4 using glacial aceticacid (requires ˜500 μl glacial acetic acid/L solution). 1 L/run is usedwith an extra 2 L for the 24-channel harvester, and 2 L/run with anextra 4 L for the 48-channel harvester, stored at room temperature.

Prepare 0.3% Polyethyleneimine (PEI) in MilliQ H₂O

Add 3 ml of 50% polyethyleneimine solution to 500 ml of MilliQ H₂O usinga 10 ml syringe. Mix solution thoroughly with a stir-rod and store atroom temperature until later use.

Prepare a 50× e Dilution Series

Prelabel 1.5 ml tubes for each of the drug dilution series and add 900μl of 10 mM TA (pH7.4 @ room temp.) to each tube. Add 100 μl of the 500mM glycine to the first tube (10⁻³M) and continue the 1:10 dilutionseries until final dilution for that compound (10⁻¹²M). Weigh outGLYX-13 for the drug dilution series (which will also range from 1×10⁻³Mto 1×10⁻¹²M) and dilute to 50 mM with 10 mM TA (pH7.4). Pipette 40 μl ofeach dilution into the appropriate reaction vial

The final concentration of DCK will be 30 μM in the reaction vial.

The final concentration of glutamate will be 50 μM in the reaction vial.For 12 runs, you will need 0.25 ml of 10 mM glutamate and 24.75 ml of 10mM TA.

Presoak Filters in the 0.3% PEI Solution

Add the Membrane Extract

Prior to adding extract to a set of 24 reaction tubes, dilute theextract to a final volume of 23.4 ml with 10 mM TA and mix by vortexingfor 1 minute, or until completely resuspended. When the filters havebeen in 0.3% PEI solution for at least 35 minutes, add 935 μl of themembrane extract to each tube (corresponding to 200 μg of rat corticalmembrane extract protein in each reaction). Briefly vortex the membraneextract with the drug dilutions. Add [³H] MK-801.

Add the [³H] MK-801

Three minutes prior to the end of the first 15 minute incubation period,remove the stock vial of [³H]MK-801 from the −20° C. freezer and add 7.8μl [³H]MK-801 (1 μCi/μ1) to a 1.5 ml tube containing 642.2 μl 10 mM TA(26× Master Mix). Return the stock vial to the freezer. (Note: only openthe [³H]MK-801 in the designated place on the work bench and change yourgloves after closing the stock vial). After returning the vial to thefreezer mix the diluted [³H]MK-801 by vortexing. Once the 15 minuteincubation period has ended, add 25 μl to each of the 24 reaction tubes,and, finally, mix the solution by vortexing on setting 3.5. Filteringthe samples through the Brandel harvester.

Add 5 ml Scintillant to Each Reaction Vial

Once the filters have been placed in the appropriate scintillation vial,add 5 ml scintillant to each vial, cap the vial, and, finally, ensurethat the filter is at the bottom of the vial. Put the [³H]MK-801 inputvial in first, followed by each of the samples in order from left toright, and top to bottom, in the mini scintillation vial tube racks, fora total of 25 tubes in each run.

As a control, add 25 μl of the diluted [³H]MK-801 stock solutiondirectly to a scintillant vial. Add 5 ml scintillant, cap, and label thevial. This will assess the raw input to each reaction vial. Discard anypipette tips or waste [³H]MK-801 in the appropriate radioactive solidwaste container. After finishing, change your gloves to prevent any [³H]contamination.

Scintillation Counting

Samples must wait at least 3 hours prior to quantitation in thescintillation counter. You can either wait three hours before startingthe machine, or you can add at least 3 hrs worth of vials containingonly scintillant (blanks) at the beginning. Use the appropriate settingson the scintillation counter to account for vial size (typically 7 mlmini-vials) and count time (typically 5 minutes).

IV. In Vitro [³H]MK-801 Potentiation Assay: Results

A glycine dose response in the presence of 50 μM glutamate is shown asfollows:

FIG. 5 shows that response to maximal glycine is typically 8000 dpm withbackground counts (in the absence of DCK) to 1500 dpm. Addition of 30 μMDCK to determine absolute background reduces these background counts to1200 dpm which translates to 4.5% background. Transformation of thetypical glycine dose response data experimental data produces is shownin FIG. 6.

GLYX-13 dose response performed using the [³H]MK-801 assay as outlinedin this protocol reproducibly produces a graph with efficacy (activity)and potency as depicted in FIG. 7.

Data obtained using the assay described above is shown in Table 2 usingthe compounds shown in Table 1.

TABLE 1 Compound Structure A-1

A-2

A-3

A-4

A-5

TABLE 2 NR2A NR2B NR2C NR2D Activity NR2A Activity NR2B Activity NR2CActivity % max Potency % max Potency % max Potency % max NR2D Cmpd.glycine logM glycine logM glycine logM glycine Potency logM A-3 58.25−10.76 35.17 −13.68 A-5 not not 29.53 −13.86 38.75 −11.68 41.34 −11.63active active

Exemplary compounds of formula (III) and (IV) and corresponding startingmaterials are also delineated in FIGS. 1-4.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

INCORPORATION BY REFERENCE

The entire contents of all patents, published patent applications,websites, and other references cited herein are hereby expresslyincorporated herein in their entireties by reference.

What is claimed is:
 1. A compound having formula (I):

and pharmaceutically acceptable salts, thereof, wherein: R¹, R², R³, andR⁴ are each independently selected from the group consisting ofhydrogen; halogen; C₁₋₆alkyl; C₁₋₆ perfluoroalkyl; C₂₋₆alkenyl;C₂₋₆alkynyl; C₃₋₆cycloalkyl; phenyl; heteroaryl including from 5 to 6ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C1-C3 alkyl), O, and S;—OR^(x); —C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂;—OC(O)R^(x); —OCO₂R^(x); —OC(O)N(R^(x))₂; —N(R^(x))₂; —NR^(x)C(O)R^(x);—NR^(x)C(O)N(R^(x))₂; —NR^(x)C(O)OR^(x); and —NR^(x)C(NR^(x))N(R^(x))₂;wherein C₁₋₆alkyl is optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen; hydroxyl; phenyl; heteroaryl including from 5 to 6 ring atomswherein 1, 2, or 3 of the ring atoms are independently selected from thegroup consisting of N, NH, N(C1-C3 alkyl), O, and S; and N(R^(x))₂; R⁵and R⁶ are independently selected from the group consisting of hydrogen;C₁-C₆ alkyl, optionally substituted by one, two or three substituentsindependently selected from the group consisting of halogen, hydroxyl,and N(R^(x))₂; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy, optionally substitutedby one, two, or three substituents independently selected from the groupconsisting of halogen, hydroxyl, phenyl, and N(R^(x))₂; and -Q-Ar,wherein Q is a bond or C₁-C₆ alkylene, optionally substituted by one,two, or three independently selected halogens, and Ar is selected fromthe group consisting of phenyl and heteroaryl including from 5 to 6 ringatoms wherein 1, 2, or 3 of the ring atoms are independently selectedfrom the group consisting of N, NH, N(C1-C3 alkyl), O, and S, whereinphenyl and heteroaryl are each optionally substituted by one, two, orthree substituents independently selected from the group consisting ofhalogen, hydroxyl, phenyl, and N(R^(x))₂; or R⁵ and R⁶, together withthe atoms to which they are attached, form a C3-C6 cycloalkyl orheterocyclyl including from 3 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C1-C3 alkyl), O, and S; wherein the C3-C6 cycloalkyl andheterocyclyl are each optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, phenyl, and N(R^(x))₂; R⁵⁵ is H, or R⁵⁵ and R⁵,together with the atoms to which they are attached, form a C3-C6cycloalkyl or heterocyclyl including from 3 to 6 ring atoms wherein 1,2, or 3 of the ring atoms are independently selected from the groupconsisting of N, NH, N(C1-C3 alkyl), O, and S; wherein the C3-C6cycloalkyl and heterocyclyl are each optionally substituted by one, two,or three substituents independently selected from the group consistingof halogen, hydroxyl, phenyl, and N(R^(x))₂; R⁷ and R⁷⁸ are eachindependently selected from the group consisting of hydrogen; C₁-C₆alkyl; C₁₋₆ perfluoroalkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy; heteroarylincluding from 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atomsare independently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; heterocyclyl including from 3 to 6 ring atoms wherein1, 2, or 3 of the ring atoms are independently selected from the groupconsisting of N, NH, N(C1-C3 alkyl), O, and S; and phenyl; wherein C₁-C₆alkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy; heteroaryl; heterocyclyl; phenylare each optionally substituted by one, two, or three substituentsindependently selected from the group consisting of halogen; hydroxyl;phenyl; heteroaryl including from 5 to 6 ring atoms wherein 1, 2, or 3of the ring atoms are independently selected from the group consistingof N, NH, N(C1-C3 alkyl), O, and S; and N(R^(x))₂; R⁸ is selected fromthe group consisting of hydrogen; halogen; hydroxyl; C₁-C₆ alkyl; C₁₋₆perfluoroalkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy; heteroaryl includingfrom 5 to 6 ring atoms wherein 1, 2, or 3 of the ring atoms areindependently selected from the group consisting of N, NH, N(C1-C3alkyl), O, and S; heterocyclyl including from 3 to 6 ring atoms wherein1, 2, or 3 of the ring atoms are independently selected from the groupconsisting of N, NH, N(C1-C3 alkyl), O, and S; and phenyl; wherein C₁-C₆alkyl; C₁-C₆ alkoxy; C₃-C₆ cycloalkoxy; heteroaryl; heterocyclyl; andphenyl are each optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, phenyl, and N(R^(x))₂; or R⁷ and R⁸, together withthe atoms to which they are attached, form C3-C6 cycloalkyl orheterocyclyl including from 3 to 6 ring atoms wherein 1, 2, or 3 of thering atoms are independently selected from the group consisting of N,NH, N(C₁-C₃ alkyl), O, and S; wherein the C₃-C₆ cycloalkyl andheterocyclyl are each optionally substituted by one, two, or threesubstituents independently selected from the group consisting ofhalogen, hydroxyl, phenyl, and N(R^(x))₂; with the proviso that at leastone of R⁷, R⁷⁸, R⁵, and R⁶ is not H; R⁹ and R¹⁰ are independentlyselected, for each occurrence, from the group consisting of hydrogen;C₁-C₆ alkyl, optionally substituted by one, two, or three substituentssubstituents independently selected from the group consisting ofhalogen, oxo, hydroxyl, phenyl, and heteroaryl including from 5 to 6ring atoms wherein 1, 2, or 3 of the ring atoms are independentlyselected from the group consisting of N, NH, N(C₁-C₃ alkyl), O, and S;C₁₋₆ perfluoroalkyl; C₂₋₆alkenyl, optionally substituted by one, two, orthree substituents substituents independently selected from the groupconsisting of halogen, oxo, and hydroxyl; C₂₋₆alkynyl, optionallysubstituted by one, two, or three substituents substituentsindependently selected from the group consisting of halogen, oxo, andhydroxyl; C₃₋₆cycloalkyl, optionally substituted by one, two, or threesubstituents substituents independently selected from the groupconsisting of C₁₋₆alkyl, C₁₋₆ perfluoroalkyl; halogen, oxo, andhydroxyl; phenyl, optionally substituted by one, two, or threesubstituents substituents independently selected from the groupconsisting of C₁₋₆alkyl; C₁₋₆ perfluoroalkyl; C₁₋₆alkoxy; halogen;hydroxyl; —C(O)R^(x); —CO₂(R^(x)); —C(O)N(R^(x))₂; —C(NR^(x))N(R^(x))₂;and —C(R^(x))₃; or R⁹ and R¹⁰, together with the nitrogen atom to whicheach is attached, form a heterocyclyl including from 3 to 6 ring atoms,which is optionally substituted by one, two, or three substituentssubstituents independently selected from the group consisting ofC₁₋₆alkyl, C₁₋₆ perfluoroalkyl; halogen, oxo, and hydroxyl; wherein whenR⁹ and R¹⁰ form a heterocyclyl including 6 ring atoms, the heterocyclyloptionally includes, in addition to the nitrogen atom attached to R⁹ andR¹⁰, a second ring heteroatom selected from the group consisting of N,NH, N(C1-C3 alkyl), O, and S; R^(x) is independently selected, for eachoccurrence, from the group consisting of hydrogen; halogen; acyl;C₁₋₆alkyl; C₁₋₆ perfluoroalkyl; and phenyl; and R^(y) is hydrogen orC₁₋₃ alkyl.
 2. A pharmaceutical composition, comprising: atherapeutically effective amount of a compound of claim 1 and apharmaceutically acceptable carrier.
 3. The pharmaceutical compositionof claim 2, wherein the composition is suitable for injection.
 4. Amethod of treating a NMDA receptor modulated disease selected fromautism in a patient in need thereof, comprising administering to thepatient a pharmaceutically effective amount of a compound of claim
 1. 5.A method of treating a NMDA receptor modulated condition selected fromthe group consisting of epilepsy, AIDS dementia, multiple systematrophy, progressive supra-nuclear palsy, Friedrich's ataxia, Down'ssyndrome, fragile X syndrome, tuberous sclerosis,olivio-ponto-cerebellar atrophy, cerebral palsy, drug-induced opticneuritis, peripheral neuropathy, myelopathy, ischemic retinopathy,diabetic retinopathy, glaucoma, cardiac arrest, behavior disorders, andimpulse control disorders, in a patient in need thereof, comprisingadministering to the patient a pharmaceutically effective amount of acompound of claim
 1. 6. A method of treating a NMDA receptor modulatedcondition selected from the group consisting of attention deficitdisorder, ADHD, schizophrenia, depression, anxiety, amelioration ofopiate, nicotine, and/or ethanol addiction, traumatic brain injury,spinal cord injury, post-traumatic stress syndrome, and Huntington'schorea, in a patient in need thereof, comprising administering to thepatient a pharmaceutically effective amount of a compound of claim
 1. 7.A method of treating a NMDA receptor modulated disease selected fromAlzheimer's disease, or memory loss that accompanies early stageAlzheimer's disease in a patient in need thereof, comprisingadministering to the patient a pharmaceutically effective amount of acompound of claim
 1. 8. A method of treating a NMDA receptor modulateddisease selected from Huntington's disease, in a patient in needthereof, comprising administering to the patient a pharmaceuticallyeffective amount of a compound of claim
 1. 9. The method of claim 4,wherein the compound is administered intravenously, intraperitoneally,intranasally, orally, intramuscularly, or subcutaneously.